Customers with multiple email aliases defined in Exchange will see all of their aliases listed in the From field if they tap the From field when composing a message:

Note, however, that although customers can select a different alias from the list, only the default alias is used for messages sent via Exchange.

Related posts:

1. iPhone, iPad, iPod touch: About the purging feature for POP email accounts
2. iPhone and iPod touch: How to configure Exchange Mail settings to increase or reduce the amount of emails displayed on the device
3. iOS 4.0: Exchange Mail, Contacts, or Calendars may not sync after update
4. iOS 4: Exchange Mail, Contacts, or Calendars may not sync after update
5. iPhone and iPod touch: Unable to locate Microsoft Exchange email attachment