Send on behalf

Set-Mailbox -Identity "administrator" -GrantSendOnBehalfTo "Cheng Angela"

https://win2.adatum.com/owa with Cheng Angela:

Set-Mailbox -Identity administrator -GrantSendOnBehalfTo "Cheng,Angela"
get-mailbox -Identity administrator | fl gr*

GrantSendOnBehalfTo : {adatum.com/TestOU/Cheng,Angela}

Set-Mailbox -Identity administrator -GrantSendOnBehalfTo Albert
get-mailbox -Identity administrator | fl gr*

GrantSendOnBehalfTo : {adatum.com/Users/albert}

To keep "Cheng,Angela", you have to:

Set-Mailbox -Identity administrator -GrantSendOnBehalfTo "Cheng,Angela","Albert"
get-mailbox -Identity administrator | fl gr*

GrantSendOnBehalfTo : {adatum.com/Users/albert, adatum.com/TestOU/Cheng,Angela}

To remove all users from the SendOnBehalf:

Set-Mailbox -Identity administrator -GrantSendOnBehalfTo $Null

Recipient Limits

Set-Mailbox -Identity "administrator" -RecipientLimits 2

Test:

Create a message with 5 recipients

You will get "This message wasn't delivered to anyone because there are too many recipients. The limit is 2. This message has 5 recipients."

Send As

Set-Mailbox -Identity Administrator -GrantSendOnBehalfTo $null

Remove-ADPermission -Identity 'CN=Administrator,CN=Users,DC=Adatum,DC=COM' -User 'Adatum\Angela.Cheng' -ExtendedRights 'Send-AS'

Angela Cheng can send email to albert@1ask2.com as administrator@1ask2.com. Albert@1ask2.com has no knowledge that the message is actually sent by Angela Cheng.

Set-Mailbox -Identity administrator -GrantSendOnBehalfTo "Cheng,Angela"

When both "Send on Behalf" and "Send As" permissions apply, "Send As" has the highest priority.

Full Access

Set-Mailbox -Identity Administrator -GrantSendOnBehalfTo $null
Remove-ADPermission -Identity 'CN=Administrator,CN=Users,DC=Adatum,DC=COM' -User 'Adatum\Angela.Cheng' -ExtendedRights 'Send-AS'

Add-MailboxPermission -Identity "CN=Administrator,CN=Users,DC=Adatum,DC=COM" -User "Adatum\Angela.Cheng" -AccessRights 'FullAccess'

Angela Cheng can open the Administrator's mailbox from outlook and OWA.

https://win2/owa/administrator@1ask2.com/

get-mailbox -RecipientTypeDetails DiscoveryMailbox | Remove-MailboxPermission -User 'Adatum\administrator' -AccessRights 'FullAccess'