Exchange 2010 Message Size Limit Issue

Here’s the Problem…

I have an external user sending an email with an 18 MB attachment to a user on my domain. The send/receive connectors are set at 25 MB. The mailbox has no delivery restriction on it so it should be defaulting to 25 MB. The external user sent the attachment to my gmail account just fine. Global settings are set to 25 MB as well. At this point I have no idea why this attachment isn’t getting delivered. It is clearly smaller than the set limits on the server.

The environment: Cloud based spam filter with message size limit of 50 MB. Windows Server 2008 R2 x64. Microsoft Exchange 2010 Standard.

(Link to the question: http://www.experts-exchange.com/Software/Server_Software/Email_Servers/Exchange/Q_27458919.html)

We have the answer!

After spending the afternoon troubleshooting message size issues for a client of ours, I have increased the message size restrictions to 25 MB on all send and receive connectors as well as the global transport rules. Exchange 2010 also has a background feature called “transport dumpster.” The default size setting for this feature is 18 MB. In the event that the message exceeds 18 MB, it will fill up the dumpster and then get rejected regardless of the size limitations in place. The best practice for this feature is to set it at 1.5 times the message size maximum. In this case, I have set it to 40 MB. This setting is configurable through either EMS or EMC.

EMS command: Set-TransportConfig –MaxDumpsterSizePerDatabase “40 MB”

In EMC it can be modified under: Organization Configuration -> Hub Transport -> Global Settings -> Transport Settings -> Properties.

Answer written By: ‘Mog’ @ Halski Systems in Gainesville, GA