Issue
When shared mailboxes are migrated from Exchange 2007 to Exchange Online via cutover or staged migration methods, they are created as user mailboxes in Exchange Online.
It is important to convert them back to shared mailboxes in Exchange Online because of licensing implications. If a mailbox isn’t licensed it will be accessible for 30 days from the mailbox creation date, after that it will be deleted automatically.
Pre-conversion state:
Get-Mailbox “Steve Test4” | fl RecipientType*
RecipientType : UserMailbox
RecipientTypeDetails : UserMailbox
Conversion
Mailboxes can be converted to shared mailboxes using the following PowerShell command. This can also be done from the Exchange admin center.
Set-Mailbox -Identity “Steve Test4” -Type Shared
Post-conversion state:
Get-Mailbox “Steve Test4” |fl RecipientType*
RecipientType : UserMailbox
RecipientTypeDetails : SharedMailbox
