Sharing a small issue that has occurred in our environment as no admin have thought about it previously.
Message size limits that are set for our environment is 25 MB but some of the sales users Complained that
they are not able to attach document to message that is more then 10 MB in size. We have tested this & found the same thing.
Issue was that in the web.config file (C:\Program Files\Microsoft\Exchange Server\ClientAccess\Sync)
<httpRuntime maxRequestLength=”10240″/> was set to 10 MB.
We have changed it to 25600(25 MB) for resolving the issue.