Tag: sendmail


Microsoft’s latest security newsletter included the fact that more than 90% of Fortune 500 companies have not fully implemented DMARC. Wow — that’s something I do at home! Worse still, the Fortune 500 company for which I work is in that 90% … a fact I hope to rectify this week. SPF is just some DNS entries that indicate the source IPs that are expected to be sending email from your domain. Lots of SPF record generators online.

DKIM is a little more involved, but it’s a lot easier now that packages for DKIM are available on Linux distro repositories. You still *can* build it from source, but it’s easier to install the OpenDKIM package.

Once the package is installed, generate the key(s) to be used with your domain(s).

cd /etc/opendkim/keys/
openssl genrsa -out dkim.private 2048
openssl rsa -in dkim.private -out dkim.public -pubout -outform PEM
# secure private key file
chown opendkim:opendkim dkim.private
chmod go-r dkim.private

Decide on the selector you are using — I use ‘mail’ as my selector. At work, I use ‘2017Q3Key’ — this allows us to change to a new key without in-transit mail being impacted. Old mail was sent with the 2017Q2 selector and *that* public key is in DNS. New mail comes across with 2017Q3 and uses the new DNS record to verify. I do *not* share these keys – anyone else sending mail from our domain needs to generate their own key (or I make one for them), use their own unique selector, and I will create the DNS records for their selector. When marketing engages a third party to send e-mails on our behalf, we have a 2017VendorName selector too.

Edit /etc/opendkim.conf. The socket line is not necessary – I just tend away from default ports as a habit. Since it’s bound to localhost, not such a big deal.

Mode sv
Socket   inet:8895@localhost
Selector mail
KeyFile /etc/opendkim/keys/dkim.private
KeyTable /etc/opendkim/KeyTable
SigningTable refile:/etc/opendkim/SigningTable
InternalHosts refile:/etc/opendkim/TrustedHosts

There’s a config option to “SendReports” — it’s a boolean that indicates if you want your system to send failure reports when the sender indicates they want such reports and provide a reporting address. Especially for testing purposes, I recommend indicating your domain wants reports — it is helpful in case you’ve got something configured not quite right and are failing delivery on some messages. As such, configure my installation to send reports. It’s additional overhead in cases where verification fails; I don’t see all that many failures, and it isn’t a lot of extra load. Since I know my installation will send detailed failure information, I can use my domain when testing new implementations.

Once you have the base configuration set, edit /etc/opendkim/SigningTable and add your domain(s) and the appropriate selector

*@rushworth.us mail._domainkey.rushworth.us
*@lisa.rushworth.us mail._domainkey.lisa.rushworth.us
*@scott.rushworth.us mail._domainkey.scott.rushworth.us
*@anya.rushworth.us mail._domainkey.anya.rushworth.us

Edit /etc/opendkim/KeyTable and map each selector from the SigningTable to a key file

mail._domainkey.rushworth.us rushworth.us:default:/etc/opendkim/keys/dkim.private
mail._domainkey.lisa.rushworth.us lisa.rushworth.us:default:/etc/opendkim/keys/lisa.dkim.private
mail._domainkey.scott.rushworth.us scott.rushworth.us:default:/etc/opendkim/keys/scott.dkim.private
mail._domainkey.anya.rushworth.us anya.rushworth.us:default:/etc/opendkim/keys/anya.dkim.private

Edit /etc/opendkim/TrustedHosts and add the internal IPs that relay your domain’s mail through the server (IP addresses or subnets)

Create DNS TXT records – the part after p= is the content of the public key file for that selector. When you are first setting up DKIM, use t=y (yes, we are just testing this). Once you confirm everything is functional, you can change to y=n (nope, really pay attention to our DKIM signature and policy). The policy is an individual preference. I use ‘all’ (all mail from my domain will be signed) and “o=-” (again all mail from my domain will be signed). You can use “o=~” (some mail from my domain is signed, some isn’t … who knows) and “dkim=unknown” (again, some is signed). You can use “dkim=discardable” (don’t just consider the message as more likely to be spam if it is not signed … you can outright drop the message). As a business, I don’t use this *just in case*. Something crazy happens – the dkim service falls over, your key gets mangled – and receiving parties can start dropping your messages. Using “dkim=all” means they are more apt to quarantine them as spam, but someone can go and get the messages. And hopefully notice something odd is happening.

mail._domainkey.domain.tld  TXT k=rsa;t=y;p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAzTnpc7tHfyH1zgT3Jx/JHmGSz8WCy1jvzu5QsYvDBmimKEHRY4Kz4mya5bOYsDQuJ/sz+BJo6xDwsUXCuyEkykIlgqP+7E9oK2EcW0dZms87SGmNEnNBN5iTe0pdzk1lXx2js3QdOWswO+cmA9F1Z8OzSR+2u79huugPFBHl79zFvOEHbigrmeHEfo0KHWpeNomf/xKx+wyYr1n3R5gS+28CeC3abSyKgmaYYRLoZsjrCLbEM0m2YPJRKd1ZGOObBMa4PZWj7pT07ISEjoNnXQ27BtcL/QjKKeLkbJ0UGEOSdPEJKuEpAUvYU9lA5hbtzrqiwdlPxWYocDVPrcqAHwIDAQAB
_adsp._domiankey.domain.tld TXT dkim=all
_domainkey.rushworth.us TXT t=y;o=-;r=dkim@lisa.rushworth.us
_ssp._domainkey.rushworth.us TXT t=y;dkim=all


Edit /etc/mail/sendmail.mc (using the port defined in /etc/opendkim.conf

INPUT_MAIL_FILTER(`dkim-filter’, `S=inet:8895@localhost’)

Make your sendmail.mc to sendmail.cf and verify that you’ve got the dkim-filter line

Xdkim-filter, S=inet:8895@localhost

Start opendkim, then restart sendmail. Now test it — inbound mail should have *their* DKIM signatures verified, outbound mail should be signed with the appropriate key.

Once you have verified your DKIM is functioning properly — well, first of all you can update your DNS records to remove testing mode. Then create your DMARC record:

_dmarc.rushworth.us     v=DMARC1; p=quarantine; sp=quarantine; rua=mailto:dmarc-rua@lisa.rushworth.us!10m; ruf=mailto:dmarc-ruf@lisa.rushworth.us!10m; rf=afrf; pct=100; ri=172800
 Again, you don’t need to use quarantine — ‘reject’ would recommend mail be dropped or ‘none’ recommends no action (good for testing). The rua (aggregate reporting email address) and ruf (address to recieve failing samples for analysis) should be in your domain.
You could add either/both “adkim=s” or “aspf=s” to indicate your DKIM or SPF adhere to strict standards. I use relaxed (default, do not need to specify it in the TXT record).
If you want the reports delivered to an address outside of your domain, that domain needs to publish a DNS record authorizing receipt of the reports:
     rushworth.us._report._dmarc.lisa.rushworth.us     v=DMARC1

Sendmail VirtUserTable

Some mail systems support sub-addressing (i.e. user+ignoredstring@domain.tld), but Exchange is not one of them. Instead of trying to sort out sub-addressing through sendmail or Exchange, we use sendmail’s virtusertable to map entire subdomains (i.e. @lisa.rushworth.us) over to our primary e-mail addresses. If an address becomes compromised, we can blacklist the particular something@subdomain.rushworth.us address in the access table).

Virtual Domain Aliases

These aliases allow changes to be made to intended recipient addresses.  There are two files required for an address to be aliased.  An entry for “VIRTUSER_DOMAIN_FILE” will exist in the sendmail.mc specifying the file listing the domains to be included for aliasing.  For us, this is /etc/mail/virtuser-domains.  This is a text file containing the name of each domain to be virtualized for aliasing, one domain per line.  Please note, the domains included herein need only be the recipient domains, not the domains to which aliases are mapped.  E.G. our virtuser-domains file contains just:


And yet we can alias test.addy@rushworth.us to lisa.landers@vibiant.dnsalias.com … it is only the source address that needs to be defined in virtuser-domains.

Aliases for the virtual domains are contained in /etc/mail/virtusertable.  The left-hand entry is the recipient address and the right-hand entry is what that recipient will be translated to.  Left-hand entries can be an email address (testaddy@rushworth.us) or a domain (@lisa.rushworth.us)

Right-hand entries can be an alternate address.  If the address should remain the same, an exclamation point can be used:

myfakeaddress@rushworth.us        external.email@domain.tld
myaddress@rushworth.us            !

The right-hand entry can also be an action, like error which will return an error code

compromised.address@lisa.rushworth.us            error:nouser User unknown


To commit changes to the virtusertable:

makemap hash /etc/mail/virtusertable.db < /etc/mail/virtusertable


Testing Virtual Aliases:

You can test the results of the virtual address space aliasing using sendmail –bt.  From within the new prompt (a greater than sign on a blank line) type3,0 followed by the address you would like to test.  E.G.:

[uid@NEOHTWNLX821 ~]# sendmail -bt
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>
> 3,0 llanders@windstream.com
canonify           input: llanders @ windstream . com
Canonify2          input: llanders < @ windstream . com >
Canonify2        returns: llanders < @ windstream . com . >
canonify         returns: llanders < @ windstream . com . >
parse              input: llanders < @ windstream . com . >
Parse0             input: llanders < @ windstream . com . >
Parse0           returns: llanders < @ windstream . com . >
ParseLocal         input: llanders < @ windstream . com . >
ParseLocal       returns: llanders < @ windstream . com . >
Parse1             input: llanders < @ windstream . com . >
Recurse            input: llanders @ valortelecom . com
canonify           input: llanders @ valortelecom . com
Canonify2          input: llanders < @ valortelecom . com >
Canonify2        returns: llanders < @ valortelecom . com . >
canonify         returns: llanders < @ valortelecom . com . >
parse              input: llanders < @ valortelecom . com . >
Parse0             input: llanders < @ valortelecom . com . >
Parse0           returns: llanders < @ valortelecom . com . >
ParseLocal         input: llanders < @ valortelecom . com . >
ParseLocal       returns: llanders < @ valortelecom . com . >
Parse1             input: llanders < @ valortelecom . com . >
Mailertable        input: < valortelecom . com > llanders < @ valortelecom . com . >
Mailertable        input: valortelecom . < com > llanders < @ valortelecom . com . >
Mailertable      returns: llanders < @ valortelecom . com . >
Mailertable      returns: llanders < @ valortelecom . com . >
MailerToTriple     input: < > llanders < @ valortelecom . com . >
MailerToTriple   returns: llanders < @ valortelecom . com . >
Parse1           returns: $# esmtp $@ valortelecom . com . $: llanders < @ valortelecom . com . >
parse            returns: $# esmtp $@ valortelecom . com . $: llanders < @ valortelecom . com . >
Recurse          returns: $# esmtp $@ valortelecom . com . $: llanders < @ valortelecom . com . >
Parse1           returns: $# esmtp $@ valortelecom . com . $: llanders < @ valortelecom . com . >
parse            returns: $# esmtp $@ valortelecom . com . $: llanders < @ valortelecom . com . >

Sendmail Mailertable

Mailertable (/etc/mail/mailertable)

Routing information for external delivery. Functionally, these are like the SMTP Connectors within Exchange. The mailertable entries can override everything including smarthost definitions. This is required for internal mail routing – our sendmail servers should not transmit email for @windstream.com to the MX records but rather the destination we intend. We also use mailertable entries to force B2B communication over internal secured channels.

If a server is unable to deliver mail to a specific domain (e.g. one of our public IP addresses gets blacklisted), a mailertable entry can be used to direct all mail destined for the domain through one of our servers still able to make delivery.

The file contains two columns, domains and actions. Domains can be ends-with substring matches:

Will match @thishost.anythingfromthisdomain.com as well as @thathost.anythingfromthisdomain.com. Domains can also be a full match of the right-hand side of the email address:

Which will match @justthisemaildomain.com. The most “accurate” match will win, not just the first match in line. So if your file contains the following:
.mysampledomain.com relay:[]
thishost.mysampledomain.com relay:[]

Mail destined for thishost.mysampledomain.com will be sent to

Actions contain both a mailer and a host. The mailer can redirect messages to local users:
.egforlocaldelivery.com local:username

Or it can force an error response:
Baddomain.com error:5.3.0:Unknown User

Our use of the mailertable, though, is to redirect mail destined for the domain:
windstream.com relay:[twnexchinbound.windstream.com]
newacquisition.com relay:[theirinternalhost.theirdomain.com]

In these cases, the square brackets around the destination override the MX record. To reroute a domain’s delivery destination, then, it is imperative that the host be enclosed in square brackets.

To commit changes to the file, either use “make” from within /etc/mail to commit all changes or the following command to commit just the changes to mailertable:
makemap hash /etc/mail/mailertable < /etc/mail/mailertable

Sendmail Configuration

Sendmail Configuration Files – sendmail.cf and sendmail.mc


Sendmail configuration files are located by default in /etc/mail/.  PureMessage uses /opt/pmx4/sendmail/etc/mail/


The main configuration file is sendmail.cf.  This is a rather cryptic file which we will not configure directly.  If you want to know the syntax for sendmail.cf, read the doc at http://www.sendmail.org or get the O’Reily book.  This information is specific to the MC file from which a macro builds the CF file..


sendmail.mc contains instructions to allow the M4 macro processor to build sendmail.cf.  Very important, before you can use a macro to create a sendmail.cf file, you need to have the macro installed.  This is the sendmail package sendmail-cf.  To ascertain if the package has been installed on RedHat:


[root@LJLLX001 mail]# rpm -qa | grep sendmail




Both sendmail and sendmail-cf packages should appear in the results.  If you do not have the CF package, install it.


The text “dnl” within sendmail.mc denotes a comment – like a tic in VisualBasic or a hash in perl.  Many lines end with dnl, or dnl with some type of commentary.  Lines beginning with dnl are not processed.


Common instructions within a sendmail.mc file:



This line refers the m4 utility to the correct “translation” to build the sendmail.cf file.  Important that the line is at the top of the mc file, but nothing to do with sendmail configuration specifically


VERSIONID(`setup for Red Hat Linux’)dnl

This line is not required, and we have ‘junk’ in it frequently.  It records the version of sendmail in the cf file for administrative reference.



More instructions for m4, different OS’s have different locations for sendmail files and the OS defined here identifies which parameters to use.  This line again needs to be at the top of the mc file



Defines which user and group sendmail will run as – do NOT pick root here.  User id 8 (mail) and group id 12 (mail) from /etc/passwd and /etc/groups respectively.


define(`confTO_CONNECT’, `1m’)dnl

Time limit for SMTP connection timeout, set to one minute normally.  This is how long your server will wait for an initial connect() to complete.



Email is normally routed by MX records.  This instruction means the ‘domain’ can also be a host name with no MX defined.  E.G.  sending email to @windstream.com will return the MX records, as they exist.  Attempting to email @neohtwnlx810.windstream.com will return no MX records, but LX810 will be contacted directly to attempt delivery.  This is a most useful instruction for return delivery to system mailers.



The sendmail class w lists the host and IP addresses for which sendmail accepts and takes local delivery.  This class can be automatically populated, or using this directive not automatically populated.  We configure this information manually in other files.


You can use a sendmail command line to determine what is set to various system variables:

[root@LJLLX001 ~]# sendmail -d0.1 -bv

Version 8.13.1





============ SYSTEM IDENTITY (after readcf) ============

(short domain name) $w             =      LJLLX001

(canonical domain name) $j        =      LJLLX001.vibiant.dnsalias.com

(subdomain name) $m                 =      vibiant.dnsalias.com

(node name) $k                             =      LJLLX001.vibiant.com




Exactly what it says – the location of procmail


define(`ALIAS_FILE’, `/etc/aliases’)dnl

Location of the file for local delivery aliases – not something we use often as there are few local delivery accounts.  In the ISP, this file can be used to give someone additional addresses which deliver to the same mailbox.  This file can also be used to direct delivery of a local account to a program – in PureMessage for example, /opt/pmx4/sendmail/etc/mail/aliases directs the pmx-auto-approve address to the application which releases user messages.


define(`confBIND_OPTS’, `WorkAroundBrokenAAAA’)dnl

This is a resolver option, it instructs sendmail to ignore SERVFAIL errors during an IPv6 lookup.  We had a few domains for which we could not deliver mail without this directive.


define(`SMART_HOST’, `[]’)

A smart host can be used instead of direct mail delivery.  For a server which is not meant to deliver mail to the internet (neohtwnlx824 for instance) the smart_host directive sends all mail to the defined destination.  The destination can be a hostname or an IP address.  Note, the mailertable will override the smarthost.


define(`STATUS_FILE’, `/var/log/mail/statistics’)dnl

Retains statistical information on server – use the command mailstats to output the statistics, the file created here is not text


define(`UUCP_MAILER_MAX’, `2000000′)dnl

Maximum size for messages relayed by UUCP mailers


define(`confPRIVACY_FLAGS’, `authwarnings,novrfy,noexpn,restrictqrun’)dnl

Disables unwanted commands – usually for security reasons.  EXPN expands groups into component members, for instance, so NOVRFY is used to disable the command.  Some of these are more important if local delivery is handled by the sendmail server.


define(`confAUTH_OPTIONS’, `A’)dnl

What kinds of authentication are supported by the server.  Useful if you are requiring authentication to relay mail, we do not do this.  Some UNIX hosts get confused if AUTH is an option made available, and you need to remark this line out of the mc file.


define(`confTO_QUEUEWARN’, `6d’)dnl

If you ever see an email from a destination mail server saying it is still trying to deliver your message and just wanted to let you know – that is what this interval defines.  To truly adhere to RFC specifications, a sendmail server should continue to attempt delivery for at least four to five days.  As a “nice” feature, the server can send periodic notifications to the sender that delivery has been delayed.  This standard comes from a time when circuits were smaller and quite lossy.  It could reasonably take days to establish a connection to the destination and transmit a message.

We are rogue and just return mail as undeliverable after a shorter period.  No reason to notify users, but to ensure that a notification is not sent, we put the warning interval at something higher than the expiration interval.


define(`confTO_QUEUERETURN’, `12h’)dnl

Related to the QUEUEWARN interval – this is the period after which the sendmail server considers the message undeliverable and returns it to the sender.  By default, this is five days so we make sure to define something more reasonable.  Otherwise there would be no way to identify “high” mail queue counts for alerting.


define(`confQUEUE_LA’, `16′)dnl

Load average at which queue only functionality is engaged


define(`confREFUSE_LA’, `48′)dnl

Load average at which SMTP connections are refused


define(`confDELAY_LA’, `30′)dnl

Load average at which sendmail will delay one second on SMTP commands


define(`confMIN_QUEUE_AGE’, `5m’)dnl

Minimum time a message has to sit in the queue before it is retried


define(`confTO_HOSTSTATUS’, `2m’)dnl

If a host has been denoted as unavailable, the status will be cached for this duration.  After the interval expires, connection to the host will be retried


define(`confMAX_DAEMON_CHILDREN’, 2000)

Maximum number of children processes permitted.  Sendmail will reject subsequent connections once this number has been reached.  Very important to have something defined on the DMZ servers.  Default is infinite and it is possible for a server to become unresponsive and need to be rebooted with out of memory errors when too many processes are spawned.


define(`confTO_IDENT’, `0′)dnl

Timeout for responses to IDENT



The default MSA options are not used, but rather explicitly defined in the DAEMON_OPTIONS directive



Shell used for command line mailing programs, not really pertinent in our case


FEATURE(`mailertable’,`hash -o /etc/mail/mailertable.db’)dnl

This file will be discussed in more detail later, this directive specifies the use of a mailertable and the location of the file.



This file will be discussed in more detail later, this directive specifies the location of the file containing virtualised domains


FEATURE(`virtusertable’,`hash -o /etc/mail/virtusertable.db’)dnl

This file will be discussed in more detail later, this directive specifies the use of virtual user mapping and the location of the file containing said mappings



Appends the local host domain to even locally delivered mail.



Alternate host names are in /etc/mail/local-host-names – machine aliases



Users who can set alternate envelope from addresses without generating a warning message.  File is /etc/mail/trusted-users


FEATURE(local_procmail,`’,`procmail -t -Y -a $h -d $u’)dnl

Specifies program to use as the local mailer, and command options


FEATURE(`access_db’,`hash -T<TMPF> -o /etc/mail/access.db’)dnl

This file will be discussed in more detail later, this directive specifies the use of an access restriction table and the location of the file.





DAEMON_OPTIONS(`Port=smtp, Name=MTA’)dnl

This is where the settings for the MSA are defined.  Port=smtp uses the default port of 25, or an alternate port can be used.  Addr=# can be included to bind sendmail to a specific address (including for localhost access only).



Defines a “milter” – mail filter.  The port and destination of the milter must be included with S=.  S=inet is a IPv4 socket, S=inet6 is an IPv6 socket, and S=local is a Unix-domain socket (/var/run/)

F= defines an action to take on failure, R (reject), T (tempfail), or if no option is included just pass the message through sendmail and ignore the milter

T= defines timeouts for sendmail’s communication with the milter:

C         Connect timeout

S          Sending timeout (sendmail transmission of data to milter)

R          Reading timeout (for reply from milter)

E          Overall timeout (between sending end of message and final ack)







This group of directives are all interrelated.  Masquerading is basically replacement – MASQUERADE_AS is the domain which will be used in place of the domains identified in MASQUERADE_DOMAIN lines.  In this case, both @arlitljl.com and @homedomain.local will be overwritten with @vibiant.dnsalias.com.  The directive FEATURE(masquerade_entire_domain) could be included to replace any subdomain of the masquerade domains (e.g. @secured.arlitljl.com, @public.arlitljl.com, and @restricted.arlitljl.com in addition to @arlitljl.com)

Masquerade envelope applies the masquerade to the envelope information and allmasquerade applies the masquerade to everything in the envelope, including cc:, from: and to: — this directive is important when we mask an acquired company’s email domain with our own.



Allows the use of domains in the MAIL FROM command to be invalid network and sender domains.  Since some people do not manage to configure their mail servers properly, we are less restrictive here to avoid complaints.



Domain(s) for which the server will accept local delivery – since our servers do not really deliver mail the domain should include the localdomain to prevent accidental misdirection of mail




Defines mailers to be used in addition to local – these should be the last lines of the mc file




When you make changes to the sendmail.mc file, you will need to run the macro processor to update the CF file.  You can see the results by running:

m4 sendmail.mc | less


The text which will be used in sendmail.cf will be displayed on the screen.  To actually commit the changes, use:

m4 sendmail.mc > sendmail.cf

or just type



Make will update all of the files in /etc/mail, so ensure you like all the changes you have made, not just the changes to sendmail.mc



Sendmail is an OpenSource SMTP mail transfer agent implemented on many different Unix platforms. The original version of sendmail, written in the early 1980’s, was written by Eric Allman at Berkeley.  The release code base of sendmail is version 8.  The packages and source can be found at http://www.sendmail.org.


Sendmail in its current iteration is configured by many individual files.  All of the configuration options available within the product are well documented at http://www.sendmail.org/doc and http://www.sendmail.org/m4/readme.html.

Future Releases:

There is not a code base 9, but rather SendmailX which has now become MeTA1 (http://www.meta1.org/).  MeTA1 does not include a local delivery agent or mail submission program – it is intended as a conduit for email only.  It will use a single configuration file with a radically different syntax.  Currently, the summer of 2007, the code is in a pre-alpha release.  So, it will be a while.


Practical Information:

We back the sendmail configuration files up nightly to NEOHTWNLX810 (/home/NDSSupport/Backups/).  You can restore the files from /etc/mail (or /opt/pmx4/sendmail/etc/mail as appropriate) to a rebuilt server and return the server’s complete configuration.


Mail Queues:

Sendmail stores unsent relayed messages in /var/spool/mqueue.  Unsent locally submitted messages will first be in /var/spool/clientmqueue.  Within the mqueue folder, each message has two separate files, one for the header information and a second for the message data.  To count the number of messages queued for delivery, then, you need to divide the number of files within /var/spool/mqueue in half:

echo `ls -al /var/spool/mqueue | wc -l` / 2 | bc


New Email Domain Configuration:

We have all of the resources required to establish a new email domain.  (Registration may well be required for a new DNS zone).  To establish a new publicly functional email domain from an existing DNS zone:

  • Create MX records within the DNS zone.  The 10 weight record should point to neohtwnlx821.windstream.com. and the 20 weight record should point to neohtwnlx823.windstream.com.  It is important in these MX records to include the period trailing the hostname
  • On NEOHTWNLX821 and NEOHTWNLX823, edit /etc/mail/access to include the new domain with RELAY
  • On NEOHTWNLX821 and NEOHTWNLX823, edit /etc/mail/mailertable to direct mail to the appropriate destination (unix host, Exchange server, etc)
    • The destination must be configured to accept email from LX821/LX823
  • If internal mail routing needs to be established, an SMTP connector needs to be added to the Exchange organization.  Additionally, mailertable entries should be created on at minimum LX825, LX830, LX833, and LX828
  • If mail should be delivered to mailboxes in the Exchange organization, the new domain should be added to the “Additional Mail Domains” recipient policy.  In this case, the SMTP connector would not be created with Exchange.


Sendmail Troubleshooting:

To display information about queued messages:

sendmail –bp

Or to obtain analysis of the domains and addresses within the mail queue, use the perl scripts located in /root/bin:

frombydomain.pl                       Ascending count of sender domains

frombyemail.pl                          Ascending count of sender email addresses

tobydomain.pl                           Ascending count of recipient domains

tobyemail.pl                              Ascending count of recipient email addresses


To retry the queues messages with output to the terminal:

sendmail –v –q –C/etc/mail/sendmail.cf &


To retry a specific recipient domain’s queue:

sendmail –v –qRthedomain.com –C/etc/mail/sendmail.cf &

Or a specific sender domain’s queue:

sendmail –v –qSthedomain.com –C/etc/mail/sendmail.cf &


To retry a specific message ID:

sendmail –v –qImsgidgoeshere –C/etc/mail/sendmail.cf &


Add “-d8.11” to the queue retry commands to output debug level diagnostic information to the terminal.  E.G.

sendmail –v -qIl6UJtCE3021014 –C/etc/mail/sendmail.cf –d 8.11


Setting Up A New Email Domain – With SenderID and DK/DKIM TXT Records

If you are going to begin using e-mail on a sub-domain of an existing zone, you do not need to do anything special to register the sub-domain. If this is a new domain, it needs to be publicly registered first. The examples used here-in will be a mail domain subordinate to windstream.com. If you are performing the tasks for a new zone, create the new zone first.

To allow e-mail exchange with a domain, create MX record(s). For a third party vendor, they need to tell you what their mail exchangers are. For internally hosted services, use the same assignments and weights from Windstream.com. As of 19 July 2017, those are:

windstream.com  MX preference = 10, mail exchanger = dell903.windstream.com

windstream.com  MX preference = 20, mail exchanger = vml905.windstream.com

windstream.com  MX preference = 110, mail exchanger = neohtwnlx821.windstream.com

Within Infoblox, you need to be using the external DNS view. You can create matching records internally – we tend not to create internal MX records as it prevents internal multi-mailer infections from routing messages. In the proper zone, click Add => Record => MX Record

The mail destination will be the subzone (here we are exchanging e-mail with @ljrtest.windstream.com)

Save this change and create the other MX records. ** You need to clue the servers into the fact this domain is now valid. ** On each server, edit /etc/mail/access and add

Ljrtest.windstream.com  RELAY

If you want to use the virtusertable to map addresses within the domain, you also need to add the domain name to /etc/mail/virtuser-domain

Finally, you need to send the mail somewhere. Edit /etc/mail/mailertable and set a relay destination of somewhere that knows about the domain and is processing mail for it (is that our Exchange server? Someone else’s Unix server? An acquired company’s mail server? … depends on what you are trying to do!)

rushworth.us    relay:[]

Save, make, and restart sendmail … now you have a fully functional external email domain.

Now secure it – that means adding sender policy framework (SPF), domain key (DK), and domain key identified mail (DKIM) records.

SPF and SenderID Records

There are both sender policy framework (v1) and SenderID (v2) records – you can create both. Not too many people use SenderID anymore, but I invariably end up finding the one guy who is evaluating mail validity purely on SenderID when I create just the SPFv1 record.

In InfoBlox, select Add => Record => TXT record. The mail destination from the MX record needs to be put in the “Name” field. Then the text value – what is that?

Quick answer is it depends. A SPF record lists all mail servers that should be sending e-mail for a domain. Is that just our MX servers? The MX servers plus the netblocks for the internal relays? Some third-party vendor?

Our MX servers and a few netblocks would be:

SPF V1: “v=spf1 mx ip4: ip4: ip4: ip4: ip4: ?all”

SPF V2: “spf2.0/pra mx ip4: ip4: ip4: ip4: ip4: ?all”

If there is a third-party vendor, they may provide an include statement for our SPF record – this is a way of referencing an external company’s SPF record within your own. You’ll see “include:mktomail.com” in our SPF records where Marketo sends mail on our behalf.

The final bit – we use ?all which means these may not be all of the servers sending mail on our behalf – we are not making an assertion beyond saying the listed sources are good. You may see vendors requesting “~all” which is a soft fail — still allows mail to pass if the sender does not match the list. The strictest is “-all” which fails mail coming from any source not in the list.

Does it matter? Depends – if a recipient has configured their mail servers to reject mail based on SPF and you use -all … mail from servers not on the list will be rejected. Not a lot of companies are thusly configured, though … so there’s not a whole lot of effective difference.

The final step is to test the SPF record. The easiest way to do so is an online SPF test site like http://tools.bevhost.com/spf/

I usually test both a host on the list and one not. The ones on the list will pass. The ones not on the list may fail (with -all) or report as neutral (?all).

DK/DKIM Records

DK and DKIM are public/private key based header signatures that assure the validity of the e-mail sender. The first thing you will need is a public/private key pair – these do not have to be trusted keys from a public certificate authority. A vendor or another internal group may provide their own public key for inclusion in our DNS record. Do not provide our private key to anyone else – keys are free, and if they are unable to generate one of their own, make one for them!

You can use openssl (openssl genrsa -out dkimkey.private 1024 followed by openssl rsa -in dkimkey.private -out dkimkey.public -pubout -outform PEM), an online generator, or the Web CA server. Once you have a key pair, you need a selector. This is because different mail servers may send mail for a domain whilst using unique private keys to sign the messages. The selector can be anything – the selector name is configured in the mail server. It is visible in the mail headers and mail logs, so don’t elect to use anything rude. Stash the private key on your mail server (or provide it to the mail server owner) and put the public key in a DNS TXT record “selectorname._domainkey.sub.domain.gTLD”. The k= indicates the key type (rsa in the openssl example), you can indicate signatures are being tested “t=y” if desired, and then paste the bits between —-BEGIN PUBLIC KEY—- and —-END PUBLIC KEY—- into the p= part.

k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA0s07391Axpsi/G0PTsO1 io1LOXSZ0bWAku4bgJ//swZj8OlFvDo59n9qC2Wsd21afI3si/PdDoDP69HNdgAT tIPaK6J0UqcCo9RNSiM3uA+GngdgTupwE2KrKn9/WQbC0tDA8e64e0HBHXwcF/ru OF+18LvpoA/cu1TFUNk0z+GSvqQ4L79k+gZWALvJL7kvCMIu3Gy8ZJpNerRSdrYH l/Nvg87dlZ+9yRI33IwNYpVl1UIrd6qLnGgM1xDMF+Sn21Obd06FOkV5ObXqKBPv 7gMhsUOPu8cIWK7wrd143wH5sWWX1VCBhhIEv1GFp6+SotvZayH5fQ/ri+BjWYzf PwIDAQAB

You should have an author domain signing practices record (_adsp._domainkey.sub.domain.gTLD) – this tells recipients what to do if a message is not signed. The content is “dkim=all” when all mail from the domain is signed. If all mail is signed and anything not signed should be dumped, then the content is “dkim=discardable”. This does not ensure that unsigned messages are discarded – that decision is up to the individual mail recipient configurations. To make no assertion, use “dkim=unknown”.

You should also have a _domainkey.sub.domain.gTLD record – you can include “t=y” when you are testing – this instructs recipients to treat signed and unsigned mail no differently. You can include notes (n=), a responsible party for the domain (r=). The important one is o= … “o=-“ means all mail from the domain should be signed, “o=~” means some mail from the domain may be unsigned.

Then test the records – you can send a message to autorespond+dkim@dk.elandsys.com and receive back a very detailed report on the DKIM validation, or you can use a web-based validation tool that checks only the DNS components.