How the software processes messages sent as / on behalf of other users

A user or a group of users may have permission to send messages as other users or on their behalf. These permissions are known as delegate permissions. See the examples below to learn which rules are applied for users sending as / on behalf of other users.

Example 1: User A has the Send As permission to User B's mailbox. When User A sends an email and enters User B's email address in the From field, the message will be considered as sent by User B. Therefore, the rules covering User B will be executed.

Example 2: User A has the Send On Behalf Of right on User B's mailbox. When User A sends an email and types the email address of User B in the From field, the message will be considered as coming from User A, and the rules covering User A will be executed.

For more information, see our Knowledge Base article.

What about emails in the Sent Items folder? Are they updated with signatures?

Please note that the Sent Items Update (SIU) feature works only with messages sent using the On Behalf of permissions to other user mailboxes. This is because the software always looks for messages to update in the Sent Items folder of a person who appears to be the sender.

When sending as, User A sends an email but it appears to be sent by User B. However, User B does not have this message in their mailbox. Therefore, the SIU service will not find it and will not update it.
In the case of send on behalf rights, a message is sent by User A on behalf of User B. The software still recognizes it properly as sent by User A and will update the mailbox of User A, as expected.

The SIU can update emails sent as a shared mailbox, if your Exchange environment is correctly configured. Learn more