I'm looking for business-class IMAP email programs to replace the traditional Outlook/POP configuration. Key features needed: the ability to access your email from any device without sacrificing features / speed. Also, the solution needs to be able to handle email for several different addresses at multiple domains.
Have you found anything good? So far the programs I've tried have been too slow, haven't had some of the automatic rules/sorting I want, etc. What would you recommend to replace a POP solution?
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Use Google Apps for Business: http://google.com/a It's inexpensive, scales like crazy, tons of space, and you can use either IMAP or of course the excellent web-based mail system.
As a bonus you also get your own calendar, doc-sharing system, etc., just like Google has anyway. If you don't need all that (I don't), it doesn't matter -- the email alone is worth it.
Gina Trapani has a nice post about how to use GMail with your domain.
The Google Apps Standard Edition includes Gmail, Google Calendar, Google Docs, and Google Sites (for simple web pages).
For small groups it's free, as already stated by Chris.
For a small set of users (< 50), you should be sure to use the standard edition, which is free. It's pretty well hidden as of late, but here's a link:
I would have added this as a comment to Jason's response (but I still cant...)
If you read the Google App's documentation it has a process to follow to facilitate the migration of all of your mail/accounts from an existing service to Google Apps.
Here it is: http://www.google.com/support/a/bin/answer.py?hl=en&answer=61369
I'm using Rackspace Email and it's pretty good, excellent support and service, and a good price. Effectively you pay $10US / month for up to 10 mailboxes, and $1/mailbox thereafter. You don't get all of the Google applications (or equivalents) but you do have some other features such as shared calendars etc.
I did investigate Google Business Apps, but in the end I just wanted to have email, so Rackspace won out.
Digital Dandelion uses Google Apps for Business. It's fantastic. I use Apple Mail and iCal perfectly with Google Apps.