Regularly I get the question from customers how to move shared mailboxes to Exchange Online and which considerations they should make before doing so. For this reason, I decided to write a little bit about this subject.
What is a shared mailbox?
A shared mailbox is used to send and receive email from a common account. A shared mailbox is available for multiple users. When someone replies an email that was sent to a shared mailbox the reply address is not the users own email address, but the email address of the shared mailbox, for example, email@example.com. The difference between a regular user mailbox and a shared mailbox is that a regular user mailbox has its own username and password, while this is not the case with a shared mailbox. Therefore, it is not possible to manually sign in to a shared mailbox.
Migrating a shared mailbox to Exchange Online
Administrators generally create a normal user mailbox and subsequently share this mailbox with different users. Doing so the mailbox will have the type “regular”. This means that the mailbox is just a normal user mailbox. Thus, after migrating this mailbox to Exchange Online, a license is required to obtain access to the mailbox. However, this is not necessary, keeping in mind that using shared mailboxes is free of charge in Exchange Online. Nevertheless, if no license is assigned, and the mailbox has the type “regular” the mailbox will be deleted after 30 days by default. To prevent that shared mailboxes will be deleted in Exchange Online without adding a license, the procedure described below can be followed.
Before start migrating, convert the mailbox type in the Exchange on premise environment so it will get the type “shared”.
Convert a user mailbox to a shared mailbox
In order to convert a user mailbox to a shared mailbox, start by checking in the on-premise Exchange environment which mailboxes do have the type “shared”. To do so follow the next steps:
First, open the Exchange Management Console -> Recipient Configuration -> Mailbox. In the column Recipient Type Details, check if the mailbox has either the type user mailbox, discovery mailbox, equipment mailbox, room mailbox or shared mailbox. Alternatively, it is possible to use PowerShell using the following command: Get-Mailbox -RecipientTypeDetails SharedMailbox
Second, convert the mailbox to the type “shared”: Set-Mailbox -Identity “email address or alias” -type shared, please see Figure 1.
Figure 1. Convert the mailbox type using PowerShell.
Now that the mailbox is converted to “Shared” it is ready for migrating to Exchange Online. After the migration check if the shared mailbox is indeed listed under shared in the Exchange admin center as presented in Figure 2.
Figure 2. Exchange admin center.
Keep in mind that the user that needs to access the shared mailbox has an Exchange Online license assigned to his or her account.