Sean Wallbridge
A colleague and I came across this issue last week while troubleshooting an incoming email issue on a client’s farm.
The Issue
Email is properly routed to the SharePoint server but then sits in the Maildrop folder. The timer job “Microsoft SharePoint Incoming E-Mail” appears to succeed but an examination of the ULS logs reveals the following error:
The Incoming E-Mail service has completed a batch. [...] Errors occurred processing […] message(s).
The Cause
This issue surfaces after the installation of the November 2014 CU or any subsequent CUs. We’ve also observed the issue after applying recent Microsoft Office Updates that apply to SharePoint (distributed through Windows Update).
The Solution
After investigation online several people report having conversations with Microsoft Support where it was indicated to them that this occurs when the “Sandbox Solutions with Code Limits” values are set to 0 points. This is set at the Site Collection Level or with a Site Collection Quota Template. Changing this value to something other than zero immediately resolved the issue and mail began being processed once again.
For more information on setting these values please refer to this MSDN article:
https://msdn.microsoft.com/en-us/library/gg615462.aspx