Hello Martin, On 2021-04-27 15:23, Martin Nadvornik wrote:
we also have the same or at least a similar problem. However not with every mail but with most. We were so far also unable to find the root cause for this and can't see any distinctive differences between mails that fail to restore and those that don't. In our specific setup piler is using a postfix server as smart host which then redirects the messages to exchange online via a transport rule. EXO accepts the restored messages our postfix sends but never delivers them to the inbox. Looking at the message trace in EXO shows that the message is beeing recived but there are no detailed trace infos available. Out first guess was also that EXO doesn't like recveiving messages with the same message ID multiple times. We haven't tried REWRITE_MESSAGE_ID yet but based on what Alex wrote this seems to not solve the problem.
Even then it would worth to check. Based on your inputs it's a pretty non-deterministic issue. If you have the time and the patience file a support issue for O365, and let's see what they have to say about it. Janos