Gmail sending

Same features are implemented for Wild Duck by zonemta-wildduck plugin

If a message is sent through Gmail MSA the following happens:

1. If similar message(*) exists in Sent Mail folder, then nothing is done
2. If there is not similar messages in Sent Mail folder then the message submitted to MSA is copied to Sent Mail with Return-Path and Received header
3. If IMAP client appends messages that have a similar message in the same folder, then the existing message is deleted and new one is appended resulting in 1234 EXPUNGE + 1234 EXISTS

(*) similar message is a message with same Message-Id and additional fields (seem to be Message-ID + Date). If the message does not look similar but has existing Message-ID then nothing is deleted. If Message-ID of the new message is unique but otherwise looks like existing message, then also nothing is deleted.