The problem stems from Outlook on Mac using Outlook Anywhere. The solution is to increase the EWS limits manually
- Open IIS from admin tools
- Navigate into
- SBS 2008: Sites / SBS Web Applications / EWS
- SBS 2011 or other: Sites / Default Web Site / EWS
- Right click on EWS and click Explore
- Make a copy of the file web.config and open the existing one in notepad.
- Find the line <httpRuntime maxRequestLength=”13280″ />, which stands for about 13mb, and change it to <httpRuntime maxRequestLength=”20000″ /> for 20mb or 50000 for 50mb, etc.
- Save the file and try again. I did not have to run resetiis or anything like that to get it working. Remember a large email can take 5-10 minutes to send.