This is probably going to sound like a stupid question so bear with me.
I have been tasked with setting up a linux pop3 email server. Simple enough. I have set one up a few times with sendmail. Here is the catch though. The only way I have ever set up an email server was to have it host the web domain as well. For example if I set up the site:
I would also set up the email server for that domain on the same system or at least the same server room.
Now I am tasked with designing the sendmail to download from someones currently existing domain thus:
Mail comes to: theirdomain.com
My server must then downloads the contents of all boxes to itself and filters for spam.
End user downloads from my server as if they were downloading from theirdomain.com.
I know this should be simple so please don't laugh too hard at my question. I just need to know the proper way to set this up so people don't kill me for not getting their mail. As a side note, should I use sendmail for this or postfix? I will be using DSPAM for the spam filtering.