We run Microsoft Small Business Server in our business, and we receive daily reports from the server on its health. Unfortunately, on Wednesday the email indicated thousands of critical errors. It only took a moment to determine that these were coming from the MSCRMExRouterService (Exchange Router).
The Exchange Router takes emails delivered to the "internal" CRM mail box and determines if it should be moved into CRM. For example, if the email has a CRM tracking token then the router will move the email into CRM.
When it is done checking on an email, that email is deleted from the mailbox.
In order to determine what was going on, I logged into the user account that hosts the internal CRM mailbox using Outlook Web Access. As soon as I went in there it was clear what the problem was. The single email that was in the inbox was unable to even be previewed in OWA!
It turns out that the email was corrupt and each time the routing service tried to handle it, it was throwing an exception and logging it. The good news is that all other emails were being processed correctly.
After deleting that email the errors quit occuring and the world became safe for CRM once again!