A cloud-based service included in Microsoft 365, delivering scalable messaging and collaboration features with simplified management and automatic updates.
Hello @Rising Flight
-AccessRights should not support the value "SendOnBehalfTo".
But you could try setting "-GrantSendOnBehalfTo" to NULL.
Set-Mailbox -Identity "******@mydomain.com" -GrantSendOnBehalfTo $null
Kind Regards
If the answer is helpful, please click "Accept Answer" and kindly upvote it.