Some internet access providers have port 25 disabled in their routers to prevent spam. If you run your own mailserver in a datacenter, you might have to enable the submission port (587) in postfix to be able to send emails from your local email client to your own mailserver.

To enable port 587, edit the file /etc/postfix/master.cf

vi /etc/postfix/master.cf

#submission inet n      -       n       -       -       smtpd

submission inet n      -       n       -       -       smtpd

/etc/init.d/postfix restart

Postfix provides with postsuper, postqueue and mailq some  shell utilitys to manage the mailqueue.

Here are some examples for common tasks:

List all messages that are in the mailqueue

postqueue -p

The output looks like this:

root@server:/# postqueue -p
-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
501CA23B43DB     2182 Thu Dec  3 14:24:39  test@yourdomain.com
(Host or domain name not found. Name service error for name=otherdomain.com type=MX: Host not found, try again)
info@otherdomain.com

-- 8 Kbytes in 1 Requests.

<strong>Delete a message by message ID</strong>
<p class="command">postsuper -d MessageID

replace MessageID with the ID of the message, e.g. 501CA23B43DB

root@server:/# postsuper -d 501CA23B43DB
postsuper: 501CA23B43DB: removed
postsuper: Deleted: 1 message

<strong>Remove emails by sender</strong>
<p class="command">mailq | tail +2 | awk 'BEGIN { RS = "" }
# $7=sender, $8=recipient1, $9=recipient2
{ if ($7 == "info@otherdomain.com" &amp;&amp; $9 == "")
print $1 }
' | tr -d '*!' | postsuper -d -

replace "info@otherdomain.com" with the sender email address.

<strong>Remove emails by recipient</strong>
<p class="command">mailq | tail +2 | awk 'BEGIN { RS = "" }
# $7=sender, $8=recipient1, $9=recipient2
{ if ($8 == "you@yourdomain.com" &amp;&amp; $9 == "")
print $1 }
' | tr -d '*!' | postsuper -d -

replace you@yourdomain.com with the recipient email address.

<strong>Remove emails by sender hostname</strong>
<p class="command">mailq | grep senderhostname | awk ‘{ print $1′} | postsuper -d -

replace the word “senderhostname” with the hostname of the email sender.

If your server has very high load and you want to temporarily move all message from the incoming queue to the hold queue, use the command:

postsuper -h ALL

to move the messages back to the incoming queue, use the command:

postsuper -r ALL

Instead of the word “ALL” you can also provide a specific message ID to move only one message to or from the hold queue. Message in the hold queue will not processed by postfix until they were requeued with postsuper -r.

More and more internet access providers are closing port 25 to reduce spam except for connections to their own mailservers. If you run your own mailserver and have problems to connect to it on port 25, you can enable port 465 (smtps) in postfix as a workaround. Edit the /etc/postfix/master.cf file:

vi /etc/postfix/master.cf

and remove the # in front of the smtps line. Example for Debain 5, change the line:

#smtps     inet  n       -       -       -       -       smtpd

to:

smtps     inet  n       -       -       -       -       smtpd

and restart postfix:

/etc/init.d/postfix restart

The following article explains the steps to compile postfix MTA with MySQL support on CentOS 5.3 as e.g. needed for ISPConfig 3.

Remove the postfix package from CentOS which does not has MySQL support:

/etc/init.d/postfix stop
rpm -e --nodeps postfix

cd /tmp
wget http://mirror.rackspace.com/CentOS/5.3/os/SRPMS/postfix-2.3.3-2.1.el5_2.src.rpm
rpm -i postfix-2.3.3-2.1.el5_2.src.rpm

vi /usr/src/redhat/SPECS/postfix.spec

%define MYSQL 0

%define MYSQL 1

yum install pcre-devel mysql-devel

rpmbuild -ba /usr/src/redhat/SPECS/postfix.spec

cd /usr/src/redhat/RPMS/x86_64
rpm -i postfix-2.3.3-2.1.x86_64.rpm

/etc/init.d/postfix start
chkconfig --levels 235 postfix on

If you get an error like:

Aug 21 12:41:03 webb4 postfix/sendmail[11234]: fatal: web1_user(12967): queue file write error

in your mail log, then the vale for message_size_limit in postfix main.cf is too low. Edit postfix main.cf:

vi /etc/postfix/main.cf

and set the message size limit to a higher value. E.g.

mesage_size_limit = 900000000

and restart postfix:

/etc/init.d/postfix restart

If there is no message_size_limit set in main.cf, just add the line.