If we add the sender to the Safe Senders List under Junk Email, we begin to receive them. What happened to the original email that was never delivered? We would like to know who else to add to our list and possibly retrieve the undelivered messages.
Exchange Server does not have a Safe Senders List, per se. What it does have is a Global Accept (and Deny) List under Connection Filtering, where you can add IP addresses of sending hosts that you trust.
Messages from those sending hosts will bypass Exchange Server's Connection Filtering (including instances when sending hosts are listed on Realtime Block Lists – if you have those configured), and the Exchange Intelligent Message Filter (IMF) – the content-filtering agent -- if you have it enabled.
By default Exchange Server does not drop email messages with attachments, nor is there any mechanism within Exchange Server to make it behave that way.
Are you sure you added the sender(s) to an Exchange Safe Senders List? Other options to look at may be your Microsoft Outlook client's Safe Senders List, antivirus software, or third-party antispam software.
We had the same problem in one of our offices -- some email (not all!?) with attachments never reached their destination. No NDR was delivered as well.
In our organization, we used a default global setting message delivery limit for receiving email of 15 MB. Although the email that was never delivered was between 5 MB and 10 MB, when we stopped using this limit, they arrived with no problem. Seems buggy…
This was the last place we looked. First we started looking for attachment blocking, spam rules, connection filtering, etc., but removing this limit was the solution.
Do you have comments on this Ask the Expert Q&A? Let us know.
Related information from SearchExchange.com: