Our current workaround is to modify the Mac TZ.

Since Exchange doesn't know about the TZ being presented (since we haven't patched it recently) and therefore is rejecting the request. Not the actual TZ that the client has configured. So, Outlook for Mac is taking some random TZ that happens to also be UTC +7 and presenting it to the Exchange server as the clients TZ. In reviewing the Mac client debug logs we see that Outlook for Mac is telling the Exchange server that the client timezone is Tomsk which is also UTC +7. Our users are in Thailand so their TZ is UTC +7. We checked the Exchange server and we find the initial autodiscover and authentication are fine but the subsequent HTTP We have multiple users that were just upgraded to Outlook for Mac 7 and they can no longer connect to Exchange (2013). My question is why does Outlook for Mac present the wrong TZ location to the Exchange server? Additional information is below. I was asked to move this question to the Technet support forum.