Sendmail

How To Flush Out All Email Messages From The Sendmail Queue

Sometimes email messages can be queued up with the Mail Transport Agent: "sendmail". The following command line can be used to manually try to immediately flush out All emails queued up by "sendmail". Even though a "sendmail" service may be running, this command is Ok to use, it will only run once and then terminate.

Try To Flush Out The Entire "sendmail" Queue:

[root@probe-222 root]# /usr/local/sbin/sendmail -q -v

How To Flush Out A Specific Email Message From The Sendmail Queue

"sendmail" can be told to only flush out certain emails from the "queue" with an additional argument to "-q". One can flush email messages that match a specific recipient's address:

Try To Flush Out A Specific "sendmail" Queued Email Message:

[root@probe-222 root]# /usr/local/sbin/sendmail -qR "securecomputing.com" -v

All queued email messages with a recipient address that matches: "securecomputing.com" will be flushed out. You can also use "-qS" to match on the "sender" and "-qI" to match on the "queue ID".

How To Configure SSL Relay for verizon.net

This following shows the procedure and config entries to facilitate using sendmail on an NST system for relay and authentication.

Problem: Verizon blocks TCP port 25, therefore a relay setup to smtp.aol.com (Verizon uses AOL email) is used. Reference: https://www.linuxquestions.org/questions/slackware-14/sendmail-smtp-auth-howto-224543/

Stop the sendmail Service

systemctl stop sendmail.service;

Create authinfo file: "/etc/mail/auth/authinfo"

Following shows contents of /etc/mail/auth/authinfo. NOTE: Change USERID and PASSWORD to the verizon.net account you will be using to send mail with.

AuthInfo:smtp.aol.com "U:USERID@verizon.net" "P:PASSWORD" "M:PLAIN"
AuthInfo: "U:USERID@verizon.net" "P:PASSWORD" "M:PLAIN"

Compile

cd "/etc/mail/auth";
makemap hash authinfo < authinfo;

Create Relay Entries

Add the following entries to the file: "/etc/mail/sendmail.mc"

define(`SMART_HOST',`smtp.aol.com')dnl
define(`RELAY_MAILER',`esmtp')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl
define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
FEATURE(`authinfo',`hash /etc/mail/auth/authinfo')dnl

Compile

cd "/etc/mail";
m4 sendmail.mc > /etc/mail/sendmail.cf;

Start the sendmail Service

systemctl start sendmail.service;

Testing

You can use the following examples to test the sendmail configuration:

echo "Test from $(hostname) on $(date)" | mailx -v -s "Test from $(hostname)" -r "FROM_EMAIL_ADDR" "TO_EMAIL_ADDR"
mail;
mailq;
tail -6 /var/log/maillog;
sendmail -d0.1 -bv;

How To Configure SSL Relay for att.net

This following shows the procedure and config entries to facilitate using sendmail on an NST system for relay and authentication on a residential AT&T Fiber connection circa 2018. It is similar to the Verizon configuration.

Problem: AT&T blocks TCP port 25, therefore a relay setup to smtp.mail.att.net is used. Reference: https://www.linuxquestions.org/questions/slackware-14/sendmail-smtp-auth-howto-224543/

Stop the sendmail Service

systemctl stop sendmail.service;

Create authinfo file: "/etc/mail/auth/authinfo"

Create the auth sub-directory (if not present).

install -d /etc/mail/auth

Following shows contents of /etc/mail/auth/authinfo. NOTE: Change USERID and PASSWORD to the att.net account you will be using to send mail with.

AuthInfo:smtp.mail.att.net "U:USERID@att.net" "P:PASSWORD" "M:PLAIN"
AuthInfo: "U:USERID@att.net" "P:PASSWORD" "M:PLAIN"

Change permissions to 600 so password can only be viewed by the root user.

chmod 600 /etc/mail/auth/authinfo

Compile

cd "/etc/mail/auth";
makemap hash authinfo < authinfo;

Create Relay Entries

Add the following entries to the file: "/etc/mail/sendmail.mc". This can go near the end of the file, but needs to be prior to the MAILER directives.

define(`SMART_HOST',`smtp.mail.att.net')dnl
define(`RELAY_MAILER',`esmtp')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 465')dnl
define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
FEATURE(`authinfo',`hash /etc/mail/auth/authinfo')dnl

Compile

cd "/etc/mail";
m4 sendmail.mc > /etc/mail/sendmail.cf;

Start the sendmail Service

systemctl start sendmail.service;
systemctl enable sendmail.service;

Testing

You can use the following examples to test the sendmail configuration:

set FROM="USER@DOMAIN"
set TO="USER@DOMAIN"
echo "Test from $(hostname) on $(date)" | mailx -v -s "Test from $(hostname)" -r "${FROM}" "${TO}"
mail;
mailq;
tail -6 /var/log/maillog;
sendmail -d0.1 -bv;