I look after two orgs of Dynamics CRM 2016 OnPrem and both orgs have the same intermittent issue, some emails are not received into the queue and the following error is logged on the mailbox:

An error occurred while creating the incoming email

Is there any additional logging on this error? There doesn't seem to be any issue with the affected emails, they are random and sometimes have attachments and some times dont. In server sync errors the error code is always 29. Microsoft does not seem to have list of error code or meanings. (That I can find?)

I am wondering if CRM stores any more useful information anywhere on why emails failed to come in. Aside from turning on tracing permanently in the production environment until the issue occurs?