Error sending AS using 365

[Jobos]

We have a shared mailbox that the admin team use using an address like [email protected]

 

We wish to send email using this address so the senders address is not revealed but on testing sending email internally works ok but externally gives an error.

 

Microsoft.Exchange.Data.Storage.SendAsDeniedException: Can't transport send message. ---> Microsoft.Mapi.MapiExceptionSendAsDenied: MapiExceptionSendAsDenied: Unable to transport send message. (hr=0x80070005, ec=1244)

 

The user has permissions on the shared mailbox, read and manage, send as

 

Is there something I've overlooked?

 

 

Thanks.

[chaplic]

Does it route out via on-prem, assuming it's a cloud mailbox or vice-versa?

[Jobos]

Does it route out via on-prem, assuming it's a cloud mailbox or vice-versa?

 

It's all cloud but I'm halfway there fixing it as the problem seems to be with the address book. When selecting the from address the email sends correctly when selecting the from address using the global address list instead of the offline global address list. The info address was hidden that might be the reason for the error, so I've made the address visible, now just need to wait for the offline address list to refresh and test again.