Apply mailbox retention policy in bulk.

Get-Mailbox -Filter { WindowsEmailAddress -like "*@≤domain-name≥" } | Set-Mailbox -RetentionPolicy "≤Policy-Name≥"

This command retrieves all mailboxes that have the retention policy applied.

Get-Mailbox -ResultSize unlimited | Where-Object {$_.RetentionPolicy -eq "≤Policy-Name≥"} | Format-Table Name,RetentionPolicy -Auto