Sysadmin Port 25 closing soon

Postfix mail server for outbound system email messages uses port 25. Usually for hosts that block port 25 I either go through webhost's unblocking criteria or use Amazon SES 3rd party SMTP in Postfix relay configuration..

Centmin Mod is provided as is so no official support for reconfiguring Postfix MTA mail server beyond what Centmin Mod initial setups up and configures for Postfix local outbound email sending.

However, if you want to sent email outbound via remote mail server like with smtp email providers like Amazon SES, PepiPost/NetcoreCloud, Mailgun, Mailjet etc there are various online guides if you search for "centos postfix relay". Instructions for Debian and Ubuntu may differ from CentOS 6 or CentOS 7 operating systems that Centmin Mod runs on so bear that in mind and read many online guides to understand the best gist of configuring Postfix relay for external mail sending via remote smtp server.

Remember, troubleshooting and setup is all on you as I provide no support, however fellow forum members are welcome to help each other out.

The following guides are a start and you should read them all and re-read them to get an understanding of what is required paying attention to differences of CentOS 6 vs CentoS 7 vs Debian/Ubuntu if any.

Note you can skip installing Postfix via yum as it's already installed

• Configure Postfix to use Gmail as a Mail Relay
• Integrating Amazon SES with Postfix - Amazon Simple Email Service (leave off the sudo in the commands used as Centmin Mod uses full root user and not sudo user)
• Integrating Postfix with Dyn’s Email Delivery
• Postfix - Mailjet Code Sample - Mailjet & Overview
  
• PepiPost/NetcoreCloud Postfix Relay

You can also setup a test VPS with a hourly billing provider and test various Postfix relay guides until you find one that works for you etc.

 

Or just request unblocking as you only use Postfix mail server for Linux system messages to yourself.

Centmin Mod installs pflogsumm command which can provide summary of postfix log entries and volume sent via command

Code (Text):

pflogsumm -d today --verbose_msg_detail /var/log/maillog

also installed is command shortcut alias for the command

Code (Text):

postfixlog

which will run same command for today's log entries
Or instead of just -d today flag, for all dates remove -d today flag

Code (Text):

pflogsumm -d today --verbose_msg_detail /var/log/maillog

I wouldn't publicly post such output though as it reveals all email addresses for sender and receiver logged by postfix so something for you to privately go through and see if you do not recognise some of the email addresses
Example output for last /var/log/maillog

Code (Text):

pflogsumm --verbose_msg_detail /var/log/maillog
Grand Totals
------------
messages
    142   received
    142   delivered
      0   forwarded
      0   deferred
      0   bounced
      0   rejected (0%)
      0   reject warnings
      0   held
      0   discarded (0%)
 160241   bytes received
 160241   bytes delivered
      1   senders
      1   sending hosts/domains
      2   recipients
      2   recipient hosts/domains
Per-Day Traffic Summary
-----------------------
    date          received  delivered   deferred    bounced     rejected
    --------------------------------------------------------------------
    Jan 26 2020        36         36
    Jan 27 2020        41         41
    Jan 28 2020        27         27
    Jan 29 2020        38         38
Per-Hour Traffic Daily Average
------------------------------
    time          received  delivered   deferred    bounced     rejected
    --------------------------------------------------------------------
    0000-0100           3          3          0          0          0
    0100-0200           1          1          0          0          0
    0200-0300           2          2          0          0          0
    0300-0400           1          1          0          0          0
    0400-0500           1          1          0          0          0
    0500-0600           2          2          0          0          0
    0600-0700           1          1          0          0          0
    0700-0800           2          2          0          0          0
    0800-0900           1          1          0          0          0
    0900-1000           2          2          0          0          0
    1000-1100           2          2          0          0          0
    1100-1200           2          2          0          0          0
    1200-1300           2          2          0          0          0
    1300-1400           2          2          0          0          0
    1400-1500           1          1          0          0          0
    1500-1600           1          1          0          0          0
    1600-1700           2          2          0          0          0
    1700-1800           2          2          0          0          0
    1800-1900           2          2          0          0          0
    1900-2000           1          1          0          0          0
    2000-2100           1          1          0          0          0
    2100-2200           2          2          0          0          0
    2200-2300           2          2          0          0          0
    2300-2400           3          3          0          0          0
Host/Domain Summary: Message Delivery
--------------------------------------
 sent cnt  bytes   defers   avg dly max dly host/domain
 -------- -------  -------  ------- ------- -----------
    137   156436        0     0.0 s    0.0 s  host.domain.com
      5     3805        0     0.4 s    0.5 s  domain.com
Host/Domain Summary: Messages Received
---------------------------------------
 msg cnt   bytes   host/domain
 -------- -------  -----------
    142   160241   host.domain.com
Senders by message count
------------------------
    142   root@host.domain.com
Recipients by message count
---------------------------
    137   root@host.domain.com
      5   username@domain.com
Senders by message size
-----------------------
 160241   root@host.domain.com
Recipients by message size
--------------------------
 156436   root@host.domain.com
   3805   username@domain.com
message deferral detail: none
message bounce detail (by relay): none
message reject detail: none
message reject warning detail: none
message hold detail: none
message discard detail: none
smtp delivery failures: none
Warnings: none
Fatal Errors: none
Panics: none
Master daemon messages: none

/var/log/mailog gets auto rotated so may not contain all postfix log dates so change the log name that pflogsumm analyses

Code (Text):

ls -lahrt /var/log/ | grep maillog
-rw-------   1 root     root             16M Jan  5 03:24 maillog-20200105
-rw-------   1 root     root            405M Jan 12 02:22 maillog-20200112
-rw-------   1 root     root            180K Jan 19 02:50 maillog-20200119
-rw-------   1 root     root            149K Jan 26 03:23 maillog-20200126
-rw-------   1 root     root             80K Jan 29 22:10 maillog

Code (Text):

pflogsumm --verbose_msg_detail /var/log/maillog-20200126

or use wildcard for all mail logs

Code (Text):

pflogsumm --verbose_msg_detail /var/log/maillog*

 

Ah I said the same thing at https://community.centminmod.com/threads/digitalocean-smtp-outbound-email-blocked-by-default.23091/