Office 365 script for giving (or recinding) send-as permissions

param($mailboxname,$user)
$mailbox = get-mailbox $mailboxname

#Give user full mailbox rights

Add-MailboxPermission -Identity $mailbox -User $user -AccessRights 'FullAccess'

#Give user send-as rights to mailbox
Add-ADPermission -Identity $mailbox.DisplayName -User $user -ExtendedRights 'Send-as'

--------------

param($mailboxname,$user)

$mailbox = get-mailbox $mailboxname

#Remove user full mailbox rights
Remove-MailboxPermission -Identity $mailbox -User $user -AccessRights 'FullAccess'

#Remove user send-as rights to mailbox
Remove-ADPermission -Identity $mailbox.DistinguishedName -User $user -ExtendedRights 'Send-as'







Article source here

http://www.exchange-powershell.com/