Actually, size of box really depends on what you want to do feature-wise. If the job of the box is just to relay mail you don't need much of a box at all. A 486 can sit on a public IP and relay mail just fine. But if you want to say, run procmail security filters on all incoming mail (ftp://ftp.rubyriver.com/pub/jhardin/antispam/procmail-security.html) you'll want a CPU that can handle the amout of mail and allow for expansion. (Still, shouldn't be overly CPU intensive. Though I have no idea of the user base.) If you're going to take it a step further and add virus scanning you're going to want a really fast CPU (maybe even dual processors?) and 10GB or more (again, depending on user base) of SCSI2/3 storage (note storage, not storage + system) Useful software here: AMaViS (A Mail Virus Scanner) http://www.amavis.org/ Architecture wise, there are good arguments for both x86 and Sun hardware. Most of the beef that will come from x86 stems from crap hardware. It's hard to go wrong with say an Intel Server board or a Dell or Compaq box. If you're going for rock solid SMP my vote is currently with Sun. People wine excessivly when they can't get their e-mail. But since you're using Excange, that negates the need for a rock solid e-mail relay box anyway. :) Kick the SMP Linux box when you kick the Exchange server and you're good. What it will come down to is your virus scanner. I don't know what's out there for Sun. There are a few for Linux, but you're not likely to find them compiled for anything but Linux x86. On the same token, it's just as likely that if you do find one for Sun it won't be compiled for anything but Solaris Sparc. (Who in their right mind runs Solaris x86...shoots a look into the machine room...when I figure out who's responsible for this thing...) I imagine that your best bet is going to be a big x86 box, running Linux (insert Debian+Postfix plug here), on a 2.2.19 kernel unless it's a SMP box or you really need IPTables. It only needs to be as stable as the Exchange server after all. :) (Weakest link, Weakest link!) Kay I'm done. -- Andrew S. Zbikowski | http://www.ringworld.org "We can learn much more from wise words, little from wisecracks and less from wise guys." --William Arthur Ward