Email sent from Shared Mailbox gets stuck in Outbox

i asked Copilot just now, and it confirms what i wrote above:

does this command 'Remove-MailboxPermission -ClearAutoMapping' achieve the same result as running 'Remove-MailboxPermission -AccessRights FullAccess' followed by 'Add-MailboxPermission AccessRights FullAccess -AutoMapping:$false'

Short answer:
Yes—using Remove-MailboxPermission -ClearAutoMapping achieves the same end state as removing a user’s FullAccess permission and then re‑adding it with -AutoMapping:$false. It clears the AutoMapping flag on the existing FullAccess ACE without removing the permission itself.