Here is a tip for those of you who use a MobileMe email address. If you would prefer to use an alias email address (which is easily set up on MobileMe), you may find it difficult to use that address when using an iPhone, iPad or iPod Touch.
The fix is this: On your IOS device, go into Settings and click on ‘Mail, Contacts, Calendars’. Select your MobileMe account and turn off the Mail component. Tap Done.
Now tap on Add New Account, then Other and finally tap Add Mail Account. Fill out the fields using your alias email address, not your main MobileMe email address.
Click Next and fill out the incoming and outgoing mail server details (mail.me.com and smtp.me.com, respectively), entering your username and password for both of these sections. Your username should be your main MobileMe email address.