User A is a Full Mailbox
User B is a Shared Mailbox
User A as "Full Access" and "Send on Behalf of" rights for User B
Send on Behalf of works fine in Outlook Mobile App and Outlook Web.
Automapping is Disabled for Shared Mailbox
User A and User B are added to Outlook Desktop as "Normal Accounts"
"Send on Behalf of" works only if a new Email address is added in the "From" field.
Both Addresses are visible in the address book.
Are we missing something?