Microsoft: Sending Email Attachment Problem with iDevices in Microsoft Exchange 2010

Problem:
Send an attachment (photo for example), and initially there's always an error popping up, "Sending this message failed". Go to outbox, hit refresh, and it sends. (9 out of 10 times). ActiveSync logging doesn't reveal anything.

Solution:
When you use certificate authentication you have to set the uploadReadAheadSize in the IIS metabase to your max email size, the default is 48KB so nearly any attachment cannot be sent/forwarded.

 With the following command you can change the value (in this case 21MB):
 C:\Windows\System32\inetsrv\appcmd.exe set config -section:system.webServer/serverRuntime /uploadReadAheadSize:"21504000" /commit:apphost

 C:\Windows\System32\inetsrv\appcmd.exe set config "Default Web Site" -section:system.webServer/serverRuntime /uploadReadAheadSize:"2150400" /commit:apphost

 After this restart the IISAdmin service to affect the change.


Reference:
1.  iPhone sending attachment problems
http://social.technet.microsoft.com/Forums/exchange/en-US/52f58b47-b95e-4f44-bb4e-6bd8b1b4eb94/iphone-sending-attachment-problems