One of the things the ACS and OpenACS community has always seemed to do is try and build a package in the current system rather than use best of breed applications from other environments.
I don't think that this is all bad most of the time (see content management) but I think that for something as complex as webmail it may be easier to try and integrate one of the other systems with OpenACS.
We are currently using Squirrell Mail (http://www.squirrellmail.org). It's a little buggy and not entirely mature. We are going to try IMP (http://www.horder.org/imp) as a substitute. Both are built in PHP and use Apache.
I am admittedly not qualified to speak about how hard it would be to mix these systems. I will only say that it seems like a real bitch to build a good webmail system from scratch, even with the headstart that OpenACS gives.
Mat, I know you said you hate integrating two languages, but would it all be easy to integrate systems that solve your problems but aren't in the same language?
talli
