Cannot send large messages via ActiveSync


When sending from a Mobile device via the ActiveSync service the device fails to send.

Some devices may return an error indicating that "The message that was sent to the server was rejected because the message was too large". (Apple iPad iOS 7). Not all mobile devices behave this way and may just keep the message in the outbox folder and retried until removed from the folder.


A global IIS restriction preventing uploads larger than 49152 Bytes.

IIS 7.5 sets a default value of 49152 Bytes for the "UploadReadAheadSize" value which limits the amount 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.

  • Navigate within IIS to the "Sites" node.
  • Determine the ID for the "MailEnable Protocols" website
  • Next navigate to the IIS log files path: C:\inetpub\logs\LogFiles
  • Locate the W3SVC(ID) folder, where ID is the number of the website ID above in step 2.
  • Sort the log files by "Date Modified' and then open the latest log files in respect to the date/time you sent the message from the mobile device.
  • Search for lines like the examples below:

2013-11-27 23:43:48 POST /Microsoft-Server-ActiveSync 443 - Apple-iPad3C4/1102.55400001 413 0 0 6396

2013-11-27 23:43:48 POST /Microsoft-Server-ActiveSync 443 - 1921.68.0.2 Apple-iPad3C4/1102.55400001 413 0 0 6396

The above log snippets report a 413 error in the line which indicates the "Request Entity is too large".


Open a Windows command prompt with administrator rights and navigate to the following location:


Run the following command:

cscript adsutil.vbs set w3svc/14/uploadreadaheadsize 51200000

Where "14" in the above command is the website ID.


Product:MailEnable (ME-6.X Pro-Any Ent-Any)
Class:TRB: Troubleshooting (Configuration or Environment)
Revised:Sunday, January 17, 2021