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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

and remove the # in front of the line:

#submission inet n – n – – smtpd

so that it looks like this:

submission inet n – n – – smtpd

and restart postfix:

/etc/init.d/postfix restart

1. Robbert says:

   January 5, 2011 at 9:56 pm

   Make sure you enable this port in your firewall settings in ISPCONFIG3 aswell. Otherwise it wont work.

   Reply
2. B. Davies says:

   February 1, 2011 at 1:55 pm

   It should work – I think , just punch in port 587 and voilla !!

   Reply
3. gboule35 says:

   February 18, 2011 at 9:40 am

   you must also create an iptables prerouting for redirect inbound port 25 to port 587.

   Reply
4. Rob says:

   February 21, 2011 at 1:50 pm

   That is not true And Would not add a benefit

   Reply
5. Mark says:

   February 5, 2012 at 5:35 am

   Great post. I have been trying to get my postfix server to accept email from external authenticated clients on both port 25 and 587 for days, and haven’t been able to get it to work. I uncommented the submission line in master.cf, and opened up port 587 on my amazon server, and it worked! If only I had found this earlier. Thanks.

   Reply