Distinguish MailDistatcher transiant and permanent errors

Upon MailDispatcher (LocalDelivery) if an email encouters an error getting stored:

• it is logged then retried 3 times then logged again.

Nothing allows distinguishing both log message, as an admin it is not easy to understand wether I did loose data or not.

Proposal:

• Change the log level upon retriesto WARN (as we did not give up yet)
• Indicate clearly if retries are performed or not in the log message.