Gmail App on Android - Sent mail stuck and not sending

This happened to me today, I replied to a mail with large attachments, and the mail got stuck in sending state, and didn't send. After reading many forums, the following fix worked for me:

1. Open Outbox
2. Select original offending message
3. Scroll to end and select REPLY, and then SAVE Draft.
4. Close Outbox and open Drafts
5. Open email and you can then access the unsent message, copy it or delete/discard it.