Exchange to 365 Migration

[ITGURU]

I have 1000 or so users I am migrating from local exchange to office 365.

I have about 10 users that have a 365 mailbox and local mailbox, but the local exchange one is used, not 365.

For migrated users sending emails to accounts which have both local and 365 accounts the emails are going to the 365 mailbox and not local

Does anyone know if using the PermanentlyClearPreviousMailboxInfo for the cloud account will mean the user will also lose all teams chats?

Theres nothing mail wise in the cloud mailbox which matters, but I believe teams chats are stored in the mailbox, however if a user currently doesnt have a 365 mailbox where would the chats be stored?

Thanks.

[chaplic]

If a user has an on-prem mailbox (and no O365 mailbox), chats are stored in a 'shadow' mailbox in O365 and when you move the mailbox to O365 contents are merged.

 

In your case if you nuke the O365 mailbox I expect you will lose the chats

[KK20]

Is there a reason they have two mailboxes? When I was migrating I simply migrated or left onsite, we are all migrated now so only service accounts that need onsite mailboxes exist onsite. However, when I was migrating, I did make some mistakes initially and accidentally ended up with an onsite + offsite mailbox, this caused no end of issues with AD IDs for that user. I think in the end I removed the 365 license and mailbox, added a license only, migrated the mailbox but needed to do some AD cleaning for that user with spurious GUIDs remaining.

 

https://docs.microsoft.com/en-us/exchange/troubleshoot/user-and-shared-mailboxes/mailbox-exists-exo-onpremises

 

If the dataflow is going to 365 (our dataflow was to onsite for our duplicate mailbox users) then I would also suggest that the teams chats will go if you kill the 365 mailbox.