Is it possible to change Return-Path in Sendmail

sendmail

I just changed Return-Path in 2 of my servers which run Exim and Posfix. The third server runs Sendmail. I spent several hours trying to find information how to change it but can not find anything. So, I need to change Return-Path so that sent emails contain Return-Path: root@mydomain.com instead of root@my-servers-hostname.com.

I can not change the server's hostname itself because my data center wants additional 5 EUR/month for a custom PTR record.

Thanks.

Best Answer

I copy from the bat book:

There must be only one Return-Path: header in any mail message, and it should be placed there by the site performing final delivery. This header should be declared in the configuration file like this:

H?P?Return-Path: $g

The ?P? flag ensures that only delivery agents that perform final delivery insert this header. Those delivery agents are usually prog and local, which usually contain an F=P delivery agent flag

So if you want to set it to something else at the bottom of your sendmail.mc add the following lines:

LOCAL_CONFIG
H?P?Return-Path: blah-blah

Also note that if this header is already defined, then it cannot be replaced unless sendmail was compiled with H_ACHECK defined for conf.c.

Where are the logs?

The default location depends on your linux/unix system, but the most common places are

/var/log/maillog
/var/log/mail.log
/var/adm/maillog
/var/adm/syslog/mail.log

If it's not there, look up /etc/syslog.conf. You should see something like this

mail.*         -/var/log/maillog

sendmail writes logs to the mail facility of syslog. Therefore, which file it gets written to depends on how syslog was configured.

If you system uses syslog-ng (instead of the more "traditional" syslog), then you'll have to look up your syslog-ng.conf file. You'll should something like this:

# This files are the log come from the mail subsystem.
#
destination mail     { file("/var/log/mail.log"); };
destination maillog  { file("/var/log/maillog"); };
destination mailinfo { file("/var/log/mail.info"); };
destination mailwarn { file("/var/log/mail.warn"); };
destination mailerr  { file("/var/log/mail.err"); };

Unable to send out emails?

One of the most common reason I've seen for a freshly installed sendmail not being able to send out emails is the DAEMON_OPTIONS being set to listen only on 127.0.0.1

See /etc/mail/sendmail.mc

dnl #
dnl # The following causes sendmail to only listen on the IPv4 loopback address
dnl # 127.0.0.1 and not on any other network devices. Remove the loopback
dnl # address restriction to accept email from the internet or intranet.
dnl #
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

If that's your case, remove the "Addr=127.0.0.1" part, rebuild your conf file and you're good to go!

DAEMON_OPTIONS(`Port=smtp, Name=MTA')dnl

[root@server]$ m4 sendmail.mc > /etc/sendmail.cf
[root@server]$/etc/init.d/sendmail restart

If you've been making changes to /etc/sendmail.cf manually thus far (instead of the *.m4 file) you can make similar changes in /etc/sendmail.cf. The offending line will look like this:

O DaemonPortOptions=Port=smtp,Addr=127.0.0.1, Name=MTA

Change it to:

O DaemonPortOptions=Port=smtp, Name=MTA

Linux – Server Sending Spam

Depending on the way your applications are set up, you may be able to see the offending user account by inspect all running processes on the server and see which user account(s) are hogging the CPU. Something like this:

ps -eo pcpu,pid,user,args | sort -k 1 -r | head -10

Hopefully it's as simple as a userspace process that's abusing known privileges and nothing like a rooted box that needs to be wiped down and rebuilt. Ready the flamethrower.

Best Answer

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