Weird behavior of message size limits in Exchange 2007
Posted on 2015-01-16
I've just seen what I think is some bizarre behavior in Exchange 2007 regarding message size limits. I'm sending from one Exchange 2007 to another Exchange 2007 in different domains. They are both Exchange 2007 SP3 with the latest rollup installed.
The sending server has no message size limits. The receiving server had a 50MB message size limit on the Internet receive connector. I got a complaint from a user at the receiving end that someone had sent him a message with a 42MB attachment and it was rejected, so I began testing.
First I checked the message size limit on all the receive connectors and found one that had a 20MB limit. I didn't think this connector should be affecting the Internet receive limits at all, but I changed it anyway. I tried sending a 43MB attachment, and it was rejected. Because they use an outside anti-spam/virus filtering service, I checked with them. They did not think their system was affecting this behavior. I had to change some log settings but finally found an SMTP log entry showing that the message was rejected at the receiving server because of the size limit.
Then, I tried resending it one more time and decided to check on the sending server. In the message queue on the SENDING server, it showed the message size as 60MB. So, I changed the receiving server's limit to 75MB, and sure enough the message went through.
Now the weirdness is that in Outlook on both the sending and receiving end, the message size shows as 43MB.
Anyone have any ideas what this is about?