Ramifications of temporarily stopping AAD Sync

Question

Doing a "Cutover Migration" from Exchange to MS365 as per https://learn.microsoft.com/en-us/exchange/mailbox-migration/cutover-migration-to-office-365.

We are currently using AAD Sync. (But not hybrid Exchange.)

At https://learn.microsoft.com/en-us/exchange/mailbox-migration/cutover-migration-to-office-365#prepare-for-a-cutover-migration is this instruction: "If you have turned on directory synchronization, you need to turn it off before you can perform a cutover migration." That links to this: https://learn.microsoft.com/en-us/microsoft-365/enterprise/turn-off-directory-synchronization?view=o365-worldwide

When I disable sync, do AAD credentials remain the same?

If I add an AD account while sync is disabled, and create a mailbox for it in Exchange using the same credentials, presumably, the mailbox will sync to MS365 via OA and be accessible by the user during migration. After migration, when I re-enable sync, will the new mailbox account "connect" to the AD account automatically?

TIA

Answer 1

@JRV Thanks for reaching out.

1) When I disable sync, do AAD credentials remain the same? Yes, it remains the same

2) If I add an AD account while sync is disabled, and create a mailbox for it in Exchange using the same credentials, presumably, the mailbox will sync to MS365 via OA and be accessible by the user during migration. After migration, when I re-enable sync, will the new mailbox account "connect" to the AD account automatically?

If you make sure that the UPN remains same and also there is no violation for the proxy address about their uniqueness (must be unique across org) Then Azure AD should Ideally match the account automatically with a feature we call Soft Match
You can read more about it here.

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