We have CRM 2016 on premise using Server-Side-Sync and the problem, that some few mails are sent with a delay of about 10 minutes.

The user sends the email from within CRM and the email changes its state to 'Pending Send', but then there is an update of the field 'postponeemailprocessinguntil' and the email is not sent instantly, but with a delay of 2 to 10 minutes. There seems to be no pattern, it happens to different users and different mailboxes, there are no workflows or plugins registered for outgoing emails. And there is no increased work to do for the server at that time.
The delay occurs for about 10 of 800 emails which are sent per day.

Has anybody experienced a similiar behavior? Does anybody know the reason why CRM sets the field postponeemailprocessinguntil or how it can be prevented from acting that way?

Some snapshot of the history (german language):
postponeemailprocessinguntil = 'Verarbeitung der E-Mail verzögern bis'
pending send = 'Senden ausstehend'