[ms office - o365] Outlook Classic - Unable to send as delgate 0x80070005-0x000004dc-0x00000524

[Frodo_Baggins]

User has send as and send on behalf of permission of a user account and is able to do so via OWA and Outlook (New) but not classic mode.

 

They were able to recently in classic Outlook but now cannot as they get a BounceBack with error 0x80070005-0x000004dc-0x00000524

 

The only other recent change which I think may be related is that we've set address book policies for each school and the mailbox the user is sending as is not in their school address book (they manually enter the email address in the send as field)

 

I've checked the usual like address is being spelt correctly, removed and re-added permissions, and re-created the Outlook profile but still get the bounce back but only in classic outlook

 

This seems to describe my issue but as mentioned the address being sent as isn't in the schools GAL A user who has Send As permission can't send email messages as another user account in Outlook in Office 365 - Microsoft Support - Is this a limitation?

Edited August 6, 2024 by Frodo_Baggins