Sync local AD to office 365 In Cloud accounts

Environment:
In Cloud accounts for all local accounts.
Existing Exchange server
O365 tenant operating as EOP
AD and O365 tenant are different names (localcompany.com, cloudcompany.com)
Azure AD Connect on another domain (DNS entries so the servers can see eachother)

"cloudcompany.com" was added as a DNS suffix to localcompany.com AD

LogonName:
In AD Users and Computers, Account tab, User Logon Name.
In the drop down there will be an option for the O365 domain. In my case, the naming convention also changed from first initial last name to firstname.lastname. I changed the User Logon Name to match what was in Office 365, first.last@cloudcompany.com

Change Display name to match:
Another convention that changed was First Last on the local AD to Last, First in the cloud. I changed the Display Name to match what is going to be in Office 365.
NOTE:
All address fields and information in the local AD will overwrite anything you already have in Office 365, so make sure the local AD is clean and has the information you want in Office 365.

created a connection rule to forward all localcompany.com email to our local server, this was in addition to the regular connection rule.

Matched Primary SMTP of local account to Cloud account.
(this is what MS says to do, doing this fucks up the connection rule forward, adding the primary cloud SMTP as an alias is all you need.)


Went through the Azure AD connect Wizard to select the OUs that had the users I wanted to sync.

Previously synched office 365 accounts, like with OKTA for example, are fubared and won't sync.(fixed later) These accounts threw errors:
This object has been updated in your Azure Active Directory, but with some modified properties, because the following attributes are associated with another object [UserPrincipalName


Also, I ended up needing the Host domain as the primary SMTP in the cloud to add to Outlook using the O365 connector in Outlook. I had originally planned to have both internal and O365 accounts in the outlook client, but the matching names messed everything up. Then I thought I'd create a new account for access to public folders, this also didn't work. It worked for the first few people, but as it scaled out it became unusable. This may be due to session limitations on individual users.


All synced users were hidden from the O365 GAL... msExchHideFromAddressLists was null, changed to False and they started showing up. This change took 24hours to complete.

Fuck this shit, never again. This migration almost made me quit.


Tips:
DO NOT do a staged migration this way. If you are going to migrate from an On Prem to the cloud, do it like a bandaid, fast and on 2. (1...2...pull...3)

Rebuilding or reconnecting Outlook autocomplete cache

either in exchange 2013+ or Office 365.

If you created a new outlook profile, I'm sure you've had complaints about 'contacts' missing. AKA the autocomplete cache.
This used to be stored in the NK2 file, stored in user\AppData\Roaming\Microsoft\Outlook\ rename as the current profile and you're done.
Microsoft holds this data on the server now, which is nice, BUT, what if you just migrated to Office365 like you have to? Because Microsoft is mother, Microsoft is father. Yes master Microsoft, I will do whatever you say. I don't need servers anymore, all must be cloud. Thank you.

Users\user\AppData\Local\Microsoft\Outlook\RoamCache\ holds a .dat file of your autocomplete
Its a super cool file name Stream_Autocomplete_absolutejibberish. It really makes it easy to find out what the new one is and what the old one was... Not.
Its easy enough to figure out which is the new autocomplete dat though, the one that's a KB and was made today, that's the new one. The old one is easy to find too. The one that wasn't made today, and has a lot of KB.

Close outlook, copy the old dat to a different folder (incase this all goes south and you have to try again, which I talk about below)
You'll want to change the old .dat filename to the new .datfile name. The file with the KBs will have the new file name. I hope that's clear... I'm reading it now and its not.
Copy the file name of the new dat, and delete new dat file. Den copy da new dat name to da old dat file and save dat shit.
Open outlook and take a look, all dat autocomplete is back.


Weird shit:
So I would do these steps, copy the new name, delete the new file, copy the new name to the old file, open outlook and watch as the Autocomplete file shrunk from 1000kb to 60kb... remember that step I said about copying the old autocomplete to a new file? Bet you wish you did that now, don't you. Close outlook, rename again and it should work. No idea why this is happening, but I seem to have to do the process twice.
Close outlook, rename, open outlook, close outlook, rename, done.