One feature seemingly missing from the iPhone mail client is the ability to send messages from an alias identity on a mail account. Suppose you have firstname.lastname@example.org, but all mailing list emails are sent to email@example.com, which is an alias for firstname.lastname@example.org. If you want to send an email from email@example.com, you would have to set up a second account, which would duplicate the firstname.lastname@example.org account emails (which is messy, in my opinion).
Now, Apple seem to have (perhaps inadvertantly) managed to enable a way of having proper aliases in iPhone OS 3.0. Essentially you need to create a list of email aliases seperated by commas in the “Address” field of the IMAP Account Information. This must be done after the account has been created with the 1 main email address, or it complains about being an invalid address. Once the account has been set up with the main email address, create a new note. In this note, type out the list of email aliases you want, starting with a comma:
highlight and copy this text to the clipboard.
Then go to “Settings > Mail, Contacts, Calendars” then choose your email account. In the address field, paste the copied text after the existing main address and save the changes. Now when you compose an email, if you click on the “From:” field, you should have an option of your main address, or any of the aliases you created.