It is fine if you control the whole ecosystem, but ironically in most scenarios where that is the case you're running Windows Active Directory anyway so therefore might have well pay a few pennies for Exchange CALs.
Compile this odd package with this patch. Now these three more. Oh they don't compile? That's right, they haven't been maintained for 3 years. Etc, etc.
It intermittently was used by different groups of about 50 people who accessed it using IMAP and the web portal without any problem.
Now all it is doing is continuing to collect email subscriptions from software vendors I was trying out at the time, though some other people may still be using it. I don't think anyone else even knew how to access the administration console, and I haven't logged into the admin console in over a year.
Occasionally, log into the shell, because of a bug I never bothered to address. It slowly collects a lot of temporary files. Speaking of which I should do that now:
`Last login: Sat Sep 1 19:27:28 2012 from __`.
Then I ran:
for i in {0..9}
do
find /tmp/jna${i}*.tmp -cmin +30 -exec rm {} \;
echo $i "out of 9" `date`
done
To answer your question: I'm sure not every module is functioning perfectly, and though it hasn't needed much maintenance over the past year, it hasn't been under much load either.
Spam control requires a little more intervention than with Gmail, but I've found it straightforward enough to set up once, then do nothing else for a couple years.