I just want some advice on what would be the best linux distubution to use for our company mail server... for the last 5 years we have been running a very old version of mandrake on a pentium 2.... time to upgrade.

Advice?

Debian Sarge.
http://www.debian.org/CD/netinst/#netinst-stable

pretty much any distro can easily be made a mail server, but you want one that will be extra stable and secure... I would recommend FreeBSD(although it's not Linux)...

If you are required to use a Linux.. I guess Debian would be a good choice...

I would do like halo14 to ease administration. Other distros are good options too depending on what you install and how well you know them.

I suggest using ssh to administrate the server and a gui sftp client when you only need to copy files on the server.
Avoid running X on a server, especially on a pentium 2 with lots of traffic, because upgrading won't do anything good in terms of speed/performance :
- kde 2. --> kde 3.4 == beautiful but slower
- gnome 2.2 --> gnome 2.12 ==beautiful but slower

However if everything is working good, i would just try applying all security updates but not upgrading because i think it is old. Surprises can happen with server configuration changes.

I wouldn't even worry about a gui sft client.. scp is much easier and equally as secure, without the hassle of connecting to the server, moving the files, disconnectings... etc..

scp <localfilename> <username>@<servername>:<filename>

by default that will stick the file in the users /home folder.