This is just a copy+paste of a comment I made on Psydone’s post over at Notion Addicts.
Mail’d (K-9 in fact) does support domains hosted on Google Apps (custom gmail domains). When you enter your account information, start with your email address and password on the wizard, and click Next. No need to go to Manual, because it goes there anyway. Next, in the detailed configuration screen, replace imap.yourdomain.org with imap.gmail.com, change the user ID wherever you find it to firstname.lastname@example.org instead of just ‘you’. Click next and do the same thing again, e.g. smtp.yourdomain.org -> smtp.gmail.com. Click next, enter your screen name and a name for the account, and you’re done!
Setting up the calendar to synchronise with Microsoft Exchange is quite easy too: look under Settings > Accounts > Add account > Calendar (with the boxy icon). It will default to Exchange settings. You also get emails synchronised from your exchange server, but curiously there is no way to find your inbox without getting a new email.
..said Exchange emails not ending up in Mail’d but in some hidden package called ‘Email’, which appears on the status bar whenever a new mail arrives.
[Update: After installing and playing around with ADW Launcher, I realised today that I could add a shortcut to the ‘Email’ program on the ADW desktop by long-pressing the screen. Now I have on demand access to Exchange email. Yay.]
[Update2: Mail’d and K-9 rely on IMAP functionality. If you want Gmail Sync, you should install Google’s Gmail application from Android Market, which is possible only after you root the Adam]