Looking for a techie who can help establish a Linux-email server for our corporate environment. Features needed are:

Ability to host 10,000 domains
ability to add POP3 accounts and alias forwarding accounts
Ability to have a web-based front end for modifying accounts
Ability to have a web-based front end for reading POP3 accounts
Ability to do SMTP with authorization (to prevent relaying)

Maybe there are off-the shelf solutions you can suggest and help install, or something to create easily. We are looking for a reliable, flexible email system to replace our NT-based system.

My suggestion for that heavy load would be qmail+vpopmail. Here's a link to a toaster that should help you out:

http://www.shupp.org/toaster/

Everything you need is there, including the web-based access. It is a bit dated though, but unless you're using glibc 2.3.1 or greater, you should be fine. If you are using glibc 2.3.1 or greater, then you will need to patch a couple of the qmail packages with the errno patches, which can be found on http://www.qmail.org/top.html. I'd also recommend reading Life with Qmail prior to ever starting. Qmail can be a pain to set up, but once you have it set it properly you can forget about it. It's rock solid, very secure, and more than capable of handling your load.