ActiveSync Message Size Limit

I received a complaint today that a user wasn’t able to send an email with multiple attachments from their iPad. They were receiving a message stating “The message was rejected by the server.” I started looking into the issue and found that the problem occurred when the user was trying to send attachments that were greater than 10MB in size. The strange thing with this is that the message limit of the environment is 50MB. I was able to replicate this issue with multiple devices connecting with ActiveSync.

Just to be sure, I checked the DB and users mailbox for any quota limits, but everything looked fine. So, I started digging deeper. What I found was a web.config file that had a message size limit setting for ActiveSync.

C:\Program Files\Microsoft\Exchange Server\v14\ClientAccess\Sync\web.config has the following lines of code:

                         <!– Allow maximum 10 megs of content –>
                         <httpRuntime madRequestLength=”10240″ />

This chunk of code is what was limiting ActiveSync devices from sending more than 10MB messages. I increased the the size to 25MB (25600) across all CAS servers and tested to make sure I could send attachments over 10MB and now everything looks great.

This was on an Exchange 2010 server, but I found a technet article related to Exchange 2013 that might give a bit more information to message size limits across an Exchange organization.