I'm looking for a way to make sure I've got a list of every mailbox and alias on my email server.
I use courier and exim4.
I produced a list from getting everything from the /home folder, but I think some addresses are missing. Is there an easy way to find out?
Without knowing exactly how you've got Exim and courier configured, there's no real way to know where the mailbox and alias lists are kept. Even the defaults vary by distribution, let alone what custom stuff you may have setup.
I'd start by going through the Exim config, looking at the transports and determine where each one delivers mail to. That should catch pretty much everything -- aliases and mailboxes.
If you're really paranoid, I'd pay someone who knows Exim to go through the config and double check your work.
If you have e.g. suffix local parts turned on in exim, then there is an infinite number of email addresses. User "bob" would have bob@domain, bob-foo@domain, bob-bar@domain, etc...
What is the /etc/aliases version for exim? Are there any exim-specific controls for aliases?
On my Postfix server, a collection of aliases from user's home directories (.forward and .forward+suffix files) as well as /etc/aliases will cover all the "normal and real" aliases.
I also have postfix configured to serve a few virtual domains, which use domain-specific mappings.
So, in answer to your question: How many virtual domains are you running, and where do they get their data?
For a simple setup, I'd go with womble's advice. If your configuration is in part built upon pattern matching (and not just upon list lookups), it is a good idea to analyze the log files for addresses/mailboxes to which mail has actually been delivered in the past n months.
