Command to count all type of mailboxes in Exchange Management Shell

Get-Mailbox -ResultSize Unlimited | measure-object

Command to count Specific type of mailboxes in Exchange Management Shell

Get-Mailbox -ResultSize Unlimited | where {$_.ResourceType -eq “Equipment”} | measure-object

Command to count mailboxes on a specific server in Exchange Management Shell

Get-Mailbox -ResultSize Unlimited | where {$_.ServerName -eq “SERVERNAME”} | measure-object