Posts Tagged ‘smtp servers’

Is it possible mail server to work on alternative port to 25?

Thursday, February 28th, 2013

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If you're running a small home based Linux or BSD server with Qmail, Exim or Postfix and it happens your ISP has filtered incoming connections to TCP/IP port 25 and you wonder if it is possible to use other alternative port to 25 for example the (Secure SMTP) SMTPS 465 supported by all major SMTP servers, the answer unfortunately is it is not possible.

The only accepted and working mail transmission port works on TCP/IP Port 25, thus the only option to make the mail server working fine is contact your ISP and convince them to remove filtering for port 25 to your custom IP. Many ISPs set a Firewall filter for 25, because nowadays many Windows XP / Vista / 7 PCs get infected with Viruses and Trojans running a tiny SMTP server on the host and trying to send million of SPAM messages via the poor unknowing victim. This congests the network and often even creates ISP network overloads, thus ISPs prefer to filter Port 25 to get rid of such eventual problems.

Once again,  alternative port to 25 for Mail is impossible !

How to disable spammer domain in QMAIL mail server with badmailto variable

Thursday, July 12th, 2012

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I've recently noticed one of the qmail SMTP servers I adminster had plenty of logged spammer emails originating from yahoo.com.tw destined to reache some random looking like emails (probably unexisting) again to *@yahoo.com.tw

The spam that is tried by the spammer is probably a bounce spam, since it seems there is no web-form or anything wrong with the qmail server that might be causing the spam troubles.
As a result some of the emails from the well configured qmail (holding SPF checks), having a correct existing MX, PTR record and even having configured Domain Keys (DKIM) started being marked, whether emails are sent to *@yahoo.com legit emails.

To deal with the shits, since we don't have any Taiwanese (tw) clients, I dediced to completely prohibit any emails destined to be sent via the mail server to *@yahoo.com.tw. This is done via /var/qmail/control/badmailto qmail control variable;

Here is content of /var/qmail/control/badmailto after banning outgoing emails to yahoo.com.tw;;;

qmail:~# cat /var/qmail/control/badmailto
[!%#:\*\^]
[\(\)]
[\{\}]
@.*@
*@yahoo.com.tw

The first 4 lines are default rules, which are solving a lot of badmailto common sent emails. Thanks God after a qmail restart:

qmail:~# qmailct restart
....

Checking in /var/log/qmail-sent/current, there are no more outgoing *@yahoo.com.tw destined emails. Problem solved …