Issue:

ActiveSync devices are not able to send e-mails sporadically. E-mails with attachment and long conversation history.

IPhone Error “Message cannot be sent” , “The message was rejected from the server”

Solution:

Browsed to configuration editor of IIS ->Microsoft-Server-ActiveSync Virtual Directory -> select ConfigurationEditor -> system.webServer -> serverRuntime -> uploadReadAheadSize.

Change value to 15728640

Recycle MSExchange ActiveSync AppPool.

Additional Info:

https://www.iis.net/configreference/system.webserver/serverruntime

• The maxRequestEntityAllowedand uploadReadAheadSize attributes respectively configure limits for the maximum number of bytes allowed in the entity body of a request and the number of bytes a Web server will read into a buffer and pass to an ISAPI extension.

https://support.microsoft.com/en-us/kb/810957