MicrosoftMicrosoftWe are in the beginning states of a 2010 to 2016 on-prem migration and ran into a real goofy intermittent problem that the fix turned out to be having to modify the migrated users primary smtp prefix to match their alias because their original prefix matched the alias of another user who has not yet been migrated ... It made absolutely no sense but we have confirmed it to be the fix. Note: I'm thinking another way to fix this would have been to change the alias on the user that had not yet been migrated but we did not test this scenario as a possible fix.
The problem was extremely intermittent and the symptom was the user who migrated to 2016 would receive "Error: Your request can't be completed right now. Please try again later" when attempting to send email from OWA and if attempting to access their calendar would receive "The calendar isn't available". Digging into the conversion via browser debugging we found that when this condition occurred we saw a response messagetext "The Client Access Server version doesn't match the mailbox server version of the resource that was being accessed. To determine the correct URL to use to access the resource, use Autodiscover with the address of the resource", a response code of "ErrorWrongServerVersion", and the MessageXml contained an Autodiscover smtpaddress of the 2010 user who had not been migrated. The 2016 mailbox in question could be using OWA for 2 days or more and not have any issues and then all of the sudden the would run into this out of the blue. I typically don't post stuff but this problem really kicked our butt and there was absolutely nothing we could find on the net that was of any help.... Maybe someone at Microsoft could shed light on what could cause the "service discovery" mention in this article to incorrectly redirect an https request for a 2016 mailbox to a 2010 mailbox whose alias matched the prefix of the smtp address of the 2016 migrated user.
