I guess this should be {to} (or am I wrong?)

The bounce is a new message that we're creating, and we're sending it back to the sender. Right? Therefore, the {to} address should be {from}. I think.

Hi,

Well, I'm not really sure, that's why I ask.

But in our case haraka was setting <> as the To: header field because the MAIL FROM (sender enveloppe) from was <> (a mailer daemon).

Setting it to {to} instead of {from} resolved the issue because then the To: header was set to the correct recipient instead of <>.

Not sure i'm really clear in explaining here :)

EDIT:
So in the mail client of the account receiving the bounce it displayed:
Sender: mailer-daemon@harakabox.tld
Recipient: "unknownadress@unknowndomain" (because of To: header set to <>)
So it means to me that the bounce used the correct return path but populated the To header with the MAIL FROM received by haraka (<>)
That's what triggered me to try {to} instead of {from}

EDIT2: this started to happen when I used the outbound.bounce_message* from the example config dir on the git. Before this it was using the "correct" To: header when boucing.

EDIT3: This seems to happen when the bouncing mail is originally from an autoresponder or mailer-daemon (which uses <> as enveloppe-sender)

Hello,

To be sure I wasn't completly out of my mind, I did a new simple test:

Scenario:

I'm sending a mail from a mailbox on a mailserver that uses haraka as outgoing gateway to relay the mail, this to an invalid recipient (the target user doesn't exists on target mail system).

Here are the bounce messages I receive:

1. When using To: {from} in the outbound.bounce_message file:
   
   Headers found in returned bounce message:

Return-Path: <>
[cut]
From: MAILER-DAEMON@mta-gw.swisscenter.net
To: <>
[cut]

2. When using To: {to} in the outbound.bounce_message file:
   

Headers found in returned bounce message:

Return-Path: <>
[cut]
From: MAILER-DAEMON@mta-gw.swisscenter.net
To: <originalsender@mailserver.ch>
[cut]

So it looks that actually {from} {to} variables actually resolves to the values from the outgoing bounce message, not the from original message.
Therefore using To: {from} resolves to <> which is the MAIL FROM of the generated bounce (and not the actual recipient of the bounce)
Using To: {to} here resolves to the recipient of the bounce (the original sender that triggered the bounce).

Does it makes sense ? It's a bit difficult for me to explain. English is not my mothertongue.

Thank you for reading :)
Kind regards