Overview

Use this when you need to a list of all mailboxes forwarding to a specified mailbox.

Simple, yet effective.

The Snippet

RecipientCN = (Get-Recipient johndoe).Identity
Get-Mailbox -ResultSize:Unlimited -Filter:{ForwardingAddress -ne $null} | Where-Object {$_.ForwardingAddress -eq $RecipientCN}

Export results to a CSV

RecipientCN = (Get-Recipient johndoe).Identity
Get-Mailbox -ResultSize:Unlimited -Filter:{ForwardingAddress -ne $null} | Where-Object {$_.ForwardingAddress -eq $RecipientCN} | Export-Csv -Path:"C:\temp\mailboxForwards.csv" -NoTypeInformation

Credit to Grant on StackOverflow for this. Huge thanks to Grant & mjolinor for answering pr0digy’s question over on Stack Overflow.