I finally figured out how to get my iPhone to use ActiveSync for Gmail, while still allowing me to use a custom reply-to address. Your mileage may vary, but here you go.
NOTE: This procedure worked for me, but may not work for you. Backup your iPhone before trying it!
(Outside the scope of this document, you must already have 2 accounts setup on your iPhone: (1) An IMAP account that is downloading email from gmail.com, and (2) an ActiveSync account that you're using to sync up Contacts and Calendars. And you must have your vanity reply-to address already registered within your Gmail account. For the purpose of this article, I'll say my vanity address is firstname.lastname@example.org.)
So, with the above as our starting point.
- Go into iPhone Settings, then click "Mail/Contacts/Calendars."
- Click on the "Fetch New Data" option.
- Scroll down and click on "Advanced."
- Set your IMAP account to "Manual."
- Set your ActiveSync account to "Push."
- Back out 2 screens so that you're on the "Mail/Contacts/Calendars" settings area.
- Click on your ActiveSync account, and then turn Mail ON. (Calendar and Contacts are probably already ON.)
- Click the "Account Info" button at the top.
- Change the "Email" field to be your vanity reply-to address, e.g. email@example.com.
- Back out 2 screens, to the "Mail/Contacts/Calendars" screen.
- Click on your IMAP account.
- Underneath "IMAP Account Information," there should be a field named "Address." Edit that field to use that same vanity address, e.g. firstname.lastname@example.org.
- Below that are 3 fields for "Incoming Mail Server." Erase the text in each of those 3 fields. (We do this so that your phone won't ever try downloading mail via IMAP.)
- Now back out to the main screen (the home screen).
- Start the Mail app, and once you're in the inbox, click the back button, and then once more until you see your 2 accounts shown.
- Click the ActiveSync account, and then click "Inbox."
If you start a new message, or reply to an existing message, it should use your email@example.com vanity address as the From: address. The gmail.com address is still exposed in the "hidden" headers, like Return-Path, but there's not much you can do about that.
NOTE: This worked for me, but may not work for you. Backup your iPhone before trying!