CRM Server Side Sync Error

Hi All,

I have server side sync configured and running on a on-premise deployment with Exchange online.

There is a forward mailbox setup and everything is working fine but at times CRM fails to process some emails with error 29 IncomingEmailRejected.

Also, I found the following error in the trace log. 

Email  for Forward Mailbox 5042f004-7b3e-e622-80d4-00155d4d6c03 was rejected because the attachment was not a valid mail item.

All the failed emails are associated with a DKIM signature.  Apart from that I cannot identify any other reason why they are not being processed by the system.

Has anyone had similar issues with DKIM emails?

Cheers,

Lasa.