I have two separate clients running Exchange 2013 and Outlook 2013 with the same issue. Neither can attach large attachments. I set the message size in the send connector to unlimited. But when I try to add large attachments it says "The File
you're attaching is bigger than the server allows." I also increased all the receive connectors to 100mb to see if that would help and it didn't have an effect. There is also no message size restriction on the test account either. I also went and added
the registry edit to remove any size restrictions for Outlook but that did not help either. I have been unable to find what in Exchange 2013 is causing this.
Vincent Sprague