[Dovecot] LMTP proxy too many DATA output timeout (perhaps)

Hi All, we are getting a lot of this message from dovecot director. They seem to be too many. Backend servers do not log anything and postfix logs a lot of these errors. It seems that dovecot strategy handgling data output timeout when proxying LMTP is or too aggressive or may have some other problem.

This error generate sometime a lot of dupicate deliveries, probably because meanwhile real server has finished delivering the mail, proxy drops the connection.

Another symptom, maybe related to duplicate uid patch, is that we are receiving blank email.

What may I look further?

Regards Luca