I work for a small business in which most employees work from home. My boss would like me to investigate the possibility of running a mail server off of one of our linux boxes (Mandrake 8.2).

I have used qmail before and got that up and running pretty quickly without any problems on my home network.

The biggest obstacle I have to overcome is the relaying issue. Most employees have different ISPs (Verizon, SBC, AOL, etc.), thus different IP ranges, etc. While most of our employees are on ISPs that don't require you to use their email address to get onto their servers, a steadily increasing minority are having to overcome these issues. From what I have read, there isn't an easy way to accomplish this.

Couple of interesting possibilities I have found are the "SMTP-after-POP" package that basically requires SMTP authentication. I think this would be ideal because then I could have a quasi-open mail realy, but not really because of the validation (ignoring the fact that passwords can be stolen or sniffed for a minute). The concern here is that I've read that some mail clients are hardwired to check the SMTP servers before the POP servers. Most of our people are on Outlook or Outlook Express. Anyone have expereince with this?

I have noticed that many modern mail clients have the option to password-authenticate SMTP servers. How might I accomplish this?

Does anyone have a better idea for how to do this? I am open to ideas and suggestions? Might procmail or sendmail be better suited to this task? Any input would be appreciated. Thanks!

I've configured a similar utility with Postfix and it works correctly. The only thing is that you should read all INSTALL etc very carefully. For example, in my program there was an option to allow IE5 to pass (without this i won't).