I really appreciate your input and I don't want to be critical.. but I am looking for only recommendations of TESTED and TRIED programs that you KNOW work well with lots of users.
The point of my post here is to reduce the number of programs I need to install and "test out". If you simply recommend whatever program you've hear of.. then this doesn't help me out. I have looked at hotscripts.com and others and have found many programs like openwebmail, etc.. there's over a hundred of them.
In other words, I'm not looking for names of programs that exist.. I'm looking for recommendation of programs that YOU are using yourself, or that you've recommended to your customers and that you KNOW work very well with many users.
Thanks everyone! (I hope this doesn't sound too harsh.. my intention wasn't to slam anyone. I just don't want to filter through a whole bunch of posts that don't really help me any more than the listings at hotscripts do.)
In order to get a refined answer you will have to unearth more information yourself.
You should find out what SMTP server and infrastructure the hosting provider uses (such as sendmail, qmail, postfix etc) and then search through the listserve archives for those MTA's
Even google will help -- queries like the following will return you something.
You will find that this subject has been discussed over and over again on the lists.
Its pointless to ask about webmail unless you know what the basic facilities are you have to work with. The underlying mail infrastructure may indeed affect what choices you have available. For example, some webmail solutions rely on the "Maildir" format, others do not.
We have been using Open WebMail for several months now, on FreeBSD and Slackware Linux servers, both running sendmail. POP3 is qpopper and pop3d. We provide it for our ISP customers, as well as our employees to access email accounts. I don't know if it qualifies as "industrial strength", but we have far more than 55 users accessing it.
As I recall, the FreeBSD install went off without a hitch. The linux install required some mods to the perl scripts, but nothing major. I'm not sure, but I think Open Webmail was written more specifically for *BSD.
Once installed and configured, it has been problem free. Like the other post, I don't know how resource intensive it is, but we would not use it if it could not do the job efficiently. It works well, looks good, customers and employees like it, and it is open source.