I am about to build a (group of?) e-mail server for a large number of users... more than 65536. Using Debian of course. :) It should include SMTP and IMAP. Users do not need to have login accounts. Probably I will be using Potato.
What should I start with? Are there good open sourced MTA and IMAP servers that do not operate on system password accounts? (so I don't have to create 60000+ accounts) For now I will be trying to distribute the accounts on more than 1 server, set-up the DNS to have more than 1 MX, and forward the mails internally through SMTP for non-existent local users. Which MTA is good for this purpose? For ease of configuration I may be choosing exim, because this is what I have been using at home (it's the default MTA for Debian.. :) I see that exim can match user names with dbm/ldap lookups as well.. which may prove useful. What about qmail or postfix? Are there other precautions that I have to take care? Are there any other precautions?