Daily Archives: August 26, 2014

Postfix in Internet, Relay in LAN

Assume the following scenario:

Your Postfix MTA is located in the Internet (having a public IP address) and you have configured an external DNS server there to be used for DNS requests.  But you are going to send mails using an internal mail server as mail relay. In this case the private IP address of the internal mail relay cannot be re-solved by the external DNS server. In this situation Postfix cannot use the mail relay and shows an error message like this below in the log file:

Aug 26 12:49:12 myclient postfix/error[28425]: B35AF34B: to=<me@company.local>, relay=none, delay=0.14, delays=0.09/0/0/0.04, dsn=4.3.5, status=deferred (delivery temporarily suspended: Host or domain name not found. Name service error for name=mailrelay.company.local type=AAAA: Host not found)

To re-solve the issue you have to add the following statement to main.cf

disable_dns_lookups = yes

and re-load postfix:

service postfix reload

Use the appropriate command to enforce delivery of queued mails.


Some useful postfix commands

To re-try delivering of queued mails:

postqueue -f

To remove all deferred mails:

postsuper -d ALL deferred

To remove all mails

postsuper -d ALL

Insufficient system resources (in reply to MAIL FROM command)

If you see an error like this while trying to send an email via your Exchange server

E32F1291C 5322 Tue Aug 26 09:15:08 MAILER-DAEMON
 (host yourexchangeserver.com[] said: 452 4.3.1 Insufficient system resources (in reply to MAIL FROM command))

then the system partition of the Exchange server has become low on free space. I have been watching this, if the free space on the drive C: of my server becomes less then 6% of the whole partition size. These are still more than 3 GByte!

You don’t need to do anything on the Exchange server but to free some additional space.