Migration from Hosted Exchange (Hybrid) to M365 Classic Outlook Client Problems and Solutions

Hello Everyone,

I'm a tech who started on a 8088 processor in the 80's.  Not mentioning the Vic20 and C64 since that hardly seem relevant!

I'm posting here to hopefully help the next person with the issues I've had over the last few weeks.  My client had to port his email from a provider with an on-perm Exchange server in a Hybrid setup with M365 to his own M365 environment.  I expected this was to be about 3 hours of work for me - setup M365 environment, plan the cut-over window, update the Outlook clients on each PC.

It ended up being roughly 20 hours of my time and at least 10 hours of dedicated time for my client.

For those wanting to jump directly to what mostly fixed it use this link, it should get you past the dreaded "an encrypted connection to your mail server is not available" when trying to add the mail account into a clean profile.

Use https://support.microsoft.com/en-us/windows/classic-outlook-troubleshooters-086e3d66-5404-4034-9cc5-545909dcc166 and pick "Classic Outlook Profile Setup Troubleshooter" 

Most hits are going to tell you its an autodiscovery issue, but if you're reading this I'm going to assume you've already confirmed that.

Our issue was some ghost configuration, only on the PCs previously setup for mail on the old server.  A new PC could add the same account without issue.  Some of the research suggested this would not happen if the proper Microsoft migration process is followed to move the account - but in our case the previous provider was unable to perform the migration.

I'll skip over the research we tried along the way, such as New Outlook Profiles, Registry entry changes, MS Personal users with the same email as MS Business Users, Autodiscover problems (including concerns that the base website for the client was offering invalid data), and so on.

After each hit where we applied a fix we again had to try adding the mail to the profile, and each time we sat watching the little circle for up to 5 minutes only to get the same error.

Now, once we found the link above - which did not come up in most searches - things got better, but not 100%.

We added the profile ok but then Outlook gave a permission error while starting.

To fix that, the user signed in must have administrative access and you use File Explorer to navigate to the folder identified in the error.  In our case it was in folders kept under \Windows\System32\.  When prompted that we need to grant permanent access we said yes.  In our case this is where Outlook was storing the ost files.

That worked for most of the clients, but we had one additional issue where the error was pointing to a folder that didn't exist.  

Just creating the folder was not enough, the final fix was to hold CTRL-SHIFT down while opening Outlook to start in administrative mode to allow it to create the ost file in the newly created folder. 

Finally 3 weeks after our cut over window, while the client had to use OWA, we were able to get outlook running.  

This was critical for my client because they did not have access to the mail history since the migration didn't happen - they had to open a copy of their PST in Outlook and use mail in OWA and constantly bounce back and forth.

I hope this helps someone avoid the pain we went though!