I have a web and mail server with Ubuntu 10.04, Apache 2, courier, postfix, Ispconfig 3 and multiple sites hosted.
The clients use mail from Outlook with a config like this:
@domain1.com use pop and smtp server mail.domain1.com
@domain2.com use pop and smtp server mail.domain2.com
@domain3.com use pop and smtp server mail.domain3.com
But some of then use mail.domain3.com, although their mails are @domain1.com or @domain2.com This works, since the different domains have the same IP, but domain3.com is going to dissapear.
¿How can I detect from the server who is using mail.domain3.com?
Mails logs didn't tell me and Apache logs only have web visits. I tried syslog and message logs too but nothing. Thanks in advance.