"Send on behalf" query

[Melpa]

Hi

Our setup is as below:

Application server (running IIS) > Sendmail relay > Exchange
(Internal)/Internet

Our mail domain is domain.com. The Sendmail relay is configured to
reject mail with a MAIL FROM: address of @domain.com (since only
Exchange should use this, not application servers).

We have an application on a server named App1 that needs to send email
on behalf of a user. So, we were thinking of using the Send on Behalf
functionality. Therefore, the application would send mail with:

From: us...@domain.com
Sender: appli...@app1.domain.com

Have I got these the right way around?

Also, we need to ensure that the MAIL FROM: is not @domain.com. Does
anyone know, when an application sends email - is the MAIL FROM:
derived from the From: or Sender:, or does this purely depend on the
application?

[Sanford Whiteman]

> From: us...@domain.com
> Sender: appli...@app1.domain.com
>
> Have I got these the right way around?

If you want to imply "sent by app on behalf of user," yes.

> Also, we need to ensure that the MAIL FROM: is not @domain.com. Does
> anyone know, when an application sends email - is the MAIL FROM:
> derived from the From: or Sender:, or does this purely depend on the
> application?

It absolutely depends on the application. The SMTP envelope (RFC x821)
and SMTP headers/body (RFC x822) standards are for the most part
independent. However, primitive SMTP APIs (PHP's mail(), .NET built-in
mail, etc.) tightly couple the two, so that, for example, when you set
the Sender: header, this becomes the envelope MAIL FROM:, and you
can't set them separately... or, similarly, you can set the MAIL
FROM:, but this is always copied to a Sender: header.

Your present API (which is what?) may well not have the flexibility
you need, but the SMTP standard certainly does.

-- Sandy

------------------------------------
Sanford Whiteman, Chief Technologist
Broadleaf Systems, a division of
Cypress Integrated Systems, Inc.
------------------------------------

[Sanford Whiteman]

> Would I be correct in stating that any replies/Out of Offices to this
> email would be sent to the From: address, yet any Non-Deliverable
> Reports would be sent to the Return-Path: address?

> Or are Out of Offices also sent to the Return-Path:?

OoO are _supposed_ to be sent to the envelope sender (not necessarily the
Return-Path: header, because an SMTP-level auto-responder is still using
the envelope information, even if a header is later added to persist the
same data).

But in reality, they are often sent to the From: address. I don't know
which are the offending messaging systems right now, but it still happens
quite a bit. RFC 3834 sets some good guidelines, but there aren't enough
MUSTs in it IMO.

You can be fairly assured that the Sender: will not be used.