I've tested and reproduced a problem that goes like this:

  • Jo is a delegate for Steve.
  • When Steve gets an invite, Jo receives a copy and accepts (or declines).
  • Jo cannot accept or decline on her Mac using Outlook 2011. (HTTP error: -18500 "The Server Could Not Fulfill The Request.)

Here are some bits of information:

  • Jo can accept/decline for Steve using Outlook 2010/2013 (PC/MAPI)
  • Jo can accept/decline for Steve using OWA.
  • Jo can accept/decline for Steve using Apple's mail.app.
  • Jo can accept/decline for other users who have set her up as a delegate from Mac/PC/OWA.
  • Other users, if set up as a Delegate for Steve, can accept/decline using Outlook 2011.
  • Jo used to be able to do this. At some point, Outlook 2011 crashed and demanded Jo rebuild her database (which she did). Thereafter the problem started.
  • I've reproduced the problem on different hardware (and, naturally, different Outlook 2011, different database, different Office identity, etc.)
  • EWS tests via Microsoft's Exchange Connectivity Tool pass.

The reason I mention Exchange 2010 is that out of all the various ways to connect, I understand that Outlook 2011 uses Exchange Web Services exclusively to interact with the Exchange server. So, this COULD be an issue with EWS or it could be a permissions issue between Jo and Steve. If I had further insight into the HTTP error, I might be able to go in a direction!

Any and all thoughts welcome!


In case anyone runs across this:

I opened up a case with Microsoft PSS.

After speaking to the SBS team for a few days -- and they did a stellar job, in my opinion -- the tech suggested we speak to the Outlook for Mac team, just in case there was something there. The OFM team had one request: Remove Jo from "Full Access" Exchange permissions on Steve's account.

Boom. That did it. Outlook 2011 (Mac) accepts/declines work fine now.

According to the OFM team, FA and Delegation permissions can conflict with one another over EWS. They have admitted that they are not doing a root-cause analysis. Perhaps, I can request that. However, I am pretty pleased and relieved that I didn't have to rebuild mailboxes or something just as onerous.

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