When a SharePoint list is being email enabled, the Central Administration service account creates a new contact object in Active Directory. When addressed directly, the object attributes configured by SharePoint are sufficient for the Exchange transport routing engine. This means that a new email sent to the email address of the email-enabled list is routed to SharePoint.
However, when the contact has been added to an Exchange distribution list, the Exchange routing engine will not resolve the contact object. You won’t see any information on this situation in the Exchange message tracking log.
The solution is pretty simple but requires the intervention of an Exchange administrator. Execute the following on the mail contact object:
Get-Contact CONTACTNAME | Set-Contact
The use of Set-Contact without any additional parameters forces Exchange to validate the currently existing attributes and the following four object attributes:
The mail contact object is a fully routable member of the Exchange organization.
Blame it on SharePoint, not Exchange.