Ever encountered the Exchange 2010 Error 18500 when sending from a Mac client?

I’ve had quite a few questions in the past with people running Macs who had issues with large file types when using Outlook 2011, so what better place to provide a solution than with a blog!

Okay, to start, I must say that we all know that the two companies involved (Microsoft and Apple) are competitors and really don’t like each other all that much. My belief is that when you use these two products together you get “Non-compatible compatibles”. Yep, you heard me right.

Let me clarify that a bit. A “Non-compatible compatible” is a client or program that “should” work and is said to be “compatible” with a competitor’s product but never works. To compound the issue, usually both companies involved point the finger at the other company as the culprit. In any case, the issue never gets solved and you feel isolated and alone. Nevertheless, that’s why we now have Google and awesome blogs to save us from these situations. Okay, now to get down off my soap box and solve your problem…

Firstly, you will need to determine what the client means by “Large file type”. There are two known issues:

  1. Can’t send above 1Meg
  2. Can’t send anything above 13Meg

If the client cannot send above 1 Meg, typically it’s a problem with the EWS folder and the authentication. You can fix this by adding Basic authentication to the EWS folder in IIS.

Open IIS under the default web site click on the EWS folder:

The EWS folder

Click on Authentication and enable the Basic Authentication:

Enable the Basic Authentication

Now if they have the 13 Meg issue, you would need to increase the Max allowed file size in the web.config file. I’ll put the directions below, however be warned, I DO NOT RECOMMEND DOING THIS for several reasons. You can cause irreparable damage to your Exchange server if done improperly. You have been warned. 

  • Change “maxAllowedContentLength” parameter in “web.config” file:From CMD change folder to “%windir%\system32\inetsrv\” and run below command:appcmd set config “Default Web Site/ews” -section:requestFiltering -requestLimits.maxAllowedContentLength:<ZZ>Note
    ZZ” is in Bytes
  • Change “maxRequestLength” parameter in “web.config” file:Open “web.config” file located in the EWS Virtual directory “Microsoft\Exchange Server\ClientAccess\exchweb\EWS“will have the following entry<httpRuntime maxRequestLength=”13280″ />Note
    By default, the max request size is approximately 13 MB.Change the item <httpRuntime maxRequestLength=”13280″ /> to <httpRuntime maxRequestLength=”KK” />Note
    Where “kk” is in Kilo Bytes.
  • Change “executionTimeout”  parameter in “web.config” file:Open web.config file located in the EWS Virtual directory “Microsoft\Exchange Server\ClientAccess\exchweb\EWS“Change the item <httpRuntime maxRequestLength=”13280″ /> to <httpRuntime executionTimeout=”X” maxRequestLength=”13280″ />Note
    Where “X” is in seconds. Example value 600 for 10 minutes. Make sure the value is greater than the time it takes to upload the file.
  • Change “connectionTimeout“settings in IIS.

Open “IIS Manager” > select “Default Web Site” > Click “Advanced Settings” > select “Connection Timeout” and change the value in Seconds (make sure the value is greater than the time it takes to upload the file)

Most people that I have encountered have chosen not to edit the web.config file and use Microsoft’s OWA to transfer large files. The question we’re left with is “why is this so difficult for Mac users and yet for Windows users it’s very easy and done via the GUI?” My guess would be we have “Non-compatible compatibles”.

If you want to send a doc larger than 13 gigs, you have to go through this process, but again, I don’t recommend it at all. If you have problems sending large docs these are the two processes that help if you’re set on sending it through outlook 2011 on a Mac, but there is risk involved so make sure you’re up for the challenge.