A customer recently contacted us because they had problems with Send As permissions not working for their Exchange Online environment. Whilst this was a relatively simple fix and a known issue, thought it worthwhile documenting it for some of our other customers as well
The first place any Admin would look is in the Exchange Admin portal > Recipients > then select the Mailbox (or Shared Mailbox if that is the case). You can then see in the Mailbox Delegation field that the permissions are correctly assigned.
So, what else could be causing the Non-Deliverable Report when trying to Send As?
This issue may occur if the address in the From box was automatically populated by using outdated, locally cached information when User A typed User B’s address. This outdated information may be used if changes to the Offline Address Book were not yet propagated to Outlook.
To resolve this issue, follow these steps:
- In the new email message in Outlook, click From, and then click Other Email Address.
- In the Send From Other E-mail Address window, click From, change the address book to the global address list (GAL), and then select the user to whose mailbox you were granted Send As permissions. For example, select User B.