Autoconnect Broken after Office 365 mailbox migration to new tenant


I have just migrated one of 3 domains from Office 365 Tenant A to Office 365 Tenant B. I can't get Outlook 2016 clients to connect to the mailboxes on the new tenant at all. I've run the Online Support and Recovery Assistant and this confirms there is an issue with Autodiscover but doesn't expand on what the issue is. Bearing in mind the external dns records remained unchanged and have been verified by the new 365 tenant, I don't see how autodiscover can be wrong.   I've tried setting up Outlook on a test PC that has never connected to the old tenant and that fails too so I don't think it's cached dns.  Anyone have any ideas what might be going on please?

Many thanks

Gavin ReidAsked:
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Vasil Michev (MVP)Commented:
I assume OWA works OK? Run the Autodiscover test from ExRCA ( or from within Outlook (hold the CTRL key -> right-click Outlooks icon in the tray -> Test E-mail autoconfiguration -> enter UPN/pass -> clear the two Guessmart checkboxes and run it), it should give you an idea what's happening.

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Gavin ReidAuthor Commented:
Hi, yes OWA works fine and we can send and receive email from it. I ran the Outlook Autodiscover test and it failed all over the place, mainly isses with XML. An example error is below:

Attempting to send an Autodiscover POST request to potential Autodiscover URLs.
Autodiscover settings weren't obtained when the Autodiscover POST request was sent.

Additional Details
Elapsed Time: 1063 ms.

Test Steps

The Microsoft Connectivity Analyzer is attempting to retrieve an XML Autodiscover response from URL for user
The Microsoft Connectivity Analyzer failed to obtain an Autodiscover XML response.

Additional Details
A Web exception occurred because an HTTP 404 - NotFound response was received from Unknown.
HTTP Response Headers:
request-id: 8cf85d5c-3000-4205-b88d-9c1b52ffdbe0
X-DiagInfo: MM1P123MB1081
X-BEServer: MM1P123MB1081
Gavin ReidAuthor Commented:
Also get this one:

Attempting to contact the Autodiscover service using the DNS SRV redirect method.
The Microsoft Connectivity Analyzer failed to contact the Autodiscover service using the DNS SRV redirect method.
Additional Details

Test Steps

Attempting to locate SRV record in DNS.
The Autodiscover SRV record wasn't found in DNS.
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Vasil Michev (MVP)Commented:
Can you try running the same test for the default alias?
Gavin ReidAuthor Commented:
Just tried running the test on the onmicrosoft address and get this:
Vasil Michev (MVP)Commented:
What's the error on the HTTP redirect method?
Gavin ReidAuthor Commented:
Hi Vasil, it looks like this issue was caused by a delay at the Microsoft end setting everything up behind the scenes, it all started working about 48 hours later, appreciate your help though thank you
Gavin ReidAuthor Commented:
Thank you
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