Connect user to different mailbox

Hi HT686 

You can disable a mailbox which disconnects it from a user account, then reattach the mailbox to a different user account. This will avoid having to export the mailbox as PST and reimport it.

https://docs.microsoft.com/en-us/Exchange/recipients/disconnected-mailboxes/disable-or-delete-mailboxes?view=exchserver-2019

https://docs.microsoft.com/en-us/Exchange/recipients/disconnected-mailboxes/connect-disabled-mailboxes?view=exchserver-2019

You might want to disconnect the invoice mailbox, disconnect Johns mailbox, then reconnect the Invoice mailbox to Johns profile. If there is nothing in Johns mailbox it can remain disconnected and will be purged from the database after 30 days by default

I would make sure you have a good Exchange backup before you do make any changes - there isn't much there that isn't reversible or fixable if you hit problems but it's always practice.

Hope this helps,

Mark