Exim posing as Sendmail: Fixing Sender and Return-Path headers

Exim

If you are having problems changing the Sender and Return-Path headers, make sure that you are editing the right configuration file. On my CentOS 5.6:

[root@server mail]# ll /usr/sbin/sendmail
lrwxrwxrwx 1 root root 21 Oct 26  2009 /usr/sbin/sendmail -> /etc/alternatives/mta
[root@server mail]# ll /etc/alternatives/mta
lrwxrwxrwx 1 root root 23 Apr  9 07:48 /etc/alternatives/mta -> /usr/sbin/sendmail.exim
[root@server mail]# ll /usr/sbin/sendmail.exim 
lrwxrwxrwx 1 root root 4 Apr  9 07:45 /usr/sbin/sendmail.exim -> exim

I spent some time trying to figure out why my changes to the sendmail.mc file were being ignored. Naturally, Exim configuration is different than Sendmail. You need to edit the /etc/exim/exim.conf file:

remote_smtp:
  driver = smtp
  return_path = bounce@domain.com
  headers_rewrite = apache@* info@domain.com s

Don't forget the "s" at the end. See this page for more information: http://www.exim.org/exim-html-2.00/doc/html/spec_32.html#SEC669

If you are OK with displaying the apache user name (ie "Sender: apache@subdomain.domain.com") in the email header, then just update the qualify_domain configuration option in the same file.

qualify_domain = domain.com

This will fix the domain only (ie "Sender: apache@domain.com").

Sendmail

If you are indeed using Sendmail, then update your /etc/mail/sendmail.mc file.

LOCAL_DOMAIN(`domain.com')dnl
MASQUERADE_AS(`domain.com')dnl
FEATURE(`masquerade_envelope')dnl
FEATURE(masquerade_entire_domain)dnl
MASQUERADE_DOMAIN(`domain.com')dnl

If this configuration file does not exist, you need to install the sendmail-cf package first. Once you are done updating all the relevant configuration options, run the following command to generate your /etc/mail/sendmail.cf file.

make -C /etc/mail

Finally, restart sendmail:

service sendmail restart