Get-MailboxLocations

Where in the world is your mailbox!

While not to be confused with Get-MailboxLocation, this function is designed to just give a count and location of the data center hosting up all your mailboxes. It does run Get-Mailbox against the entire online tenant, so that process could take a while depending on the number of mailboxes you are requesting.

For my 13 mailboxes in a test tenant, this shows the different data center locations of the mailboxes and that they are hosted on 13 different servers. For more additional complete detail, use the Get-MailboxLocation cmdlet to discover the information per mailbox.