Send As vs Send on Behalf

Overview

Send As and Send on Behalf are two Outlook permissions that let a delegate send email from someone else’s mailbox. With Send As, the email appears to come directly from the mailbox owner, with no sign of the delegate. With Send on Behalf, the From line shows that the delegate sent it on behalf of the owner. The two permissions also affect which signature Opensense applies.

Applies to routed deployments

This applies only to routed solutions that use the Plain Text Block or Stamping, not to Visual Preview.

Comparing the two permissions

Feature	Send As	Send on Behalf
How the email appears	Sent directly by the mailbox owner, with no mention of the delegate.	Shows that the delegate sent it on behalf of the mailbox owner.
Use it when	The email must appear to come only from the owner.	You need to be open about the delegation.
Envelope sender (SMTP From)	The owner's address	The delegate's address
From header	The owner's address	Delegate on behalf of Owner
Example: Jack sends for Susie	Envelope sender and From header are both Susie@company.com. Susie's signature is used.	Envelope sender is Jack@company.com. The From header shows "Jack on behalf of Susie".
Opensense setup	Turn on Use email body From: header, so the owner's signature is applied.	Test that Opensense applies the intended signature.

Setting up Opensense for Send As

With Send As, a delegate sends email as though the mailbox owner sent it. For example, Jack has Send As permission for Susie’s mailbox. When Jack uses it, the email appears to come from Susie, and Opensense should apply Susie’s signature.

1. In the Opensense portal, go to Domain Settings.
2. Turn on Use email body From: header.

Opensense then identifies the correct user, Susie in this example, from the From field in the email body, and applies her signature.

Send on Behalf and Opensense signatures

With Send on Behalf, the From line shows that the delegate sent the email on behalf of the mailbox owner, for example “Jack on behalf of Susie”.

Test Send on Behalf signatures

Email sent on behalf of a mailbox owner carries the delegate’s identity in the email headers, which can affect which signature Opensense applies. Test it, and confirm that Opensense applies the intended signature.

Envelope sender vs From header

The difference between the two senders matters when you set up email signatures:

Envelope sender (SMTP From)

The actual sender at the transport level, used in the SMTP transaction for routing and delivery. It appears in the email header as smtp.mailfrom=email.com.

From header

Who the recipient sees as the sender. It can show "Jack on behalf of Susie" with Send on Behalf, or just Susie's name with Send As.

Additional resources

• Microsoft Support: Allow someone else to manage your mail and calendar
• Send As vs Send on Behalf vs Full Access

What’s next

• Shared mailbox vs user mailbox: the two kinds of mailbox that delegates send from.
• Expected behaviors in routed Outlook Add-in deployments: how the Outlook Add-in handles sender identity when routing email.