modify.dkim.require_sender_match doesn't do anything in practice

[drdaeman]

My apologies for not following the bug report template. This is a bug I've spotted by reading the source code, not running Maddy in production - I'm trying to replace an ancient Postfix server and still figuring out the configuration I need, using source as a supplemental documentation.

I believe modify.dkim's require_sender_match setting is not doing anything. The setting is recognized, but all it does is creation of empty struct{}{}s in Modifier.senderMatch, with this field not referenced anywhere else. To best of my awareness, it's simply not used. Unit tests only ever use "off" as a value.

Before 9915c8a there used to be a shouldSign function that did some checks, but those checks were lost during the overhaul.

The dysfunctionality is probably harmless, as it's a responsibility of check.authorize_sender module to perform the proper authorization checks. Nonetheless, to avoid confusion and possible false expectations I would suggest entirely removing senderMatch struct field and adding a depreciation warning upon seeing require_sender_match, saying that this setting is non-functional.

Thank you!

[foxcpp]

You are right - check.authorize_sender replaced require_sender_match and should have been removed back then.

[cuu508]

require_sender_match is still mentioned in docs here: https://maddy.email/reference/modifiers/dkim/

Additionally, for each messages From header is checked to match MAIL FROM and authorization identity (username sender is logged in as). This can be controlled using require_sender_match directive.

Syntax: sign_subdomains boolean
Default: no
Sign emails from subdomains using a top domain key.
Allows only one domain to be specified (can be workarounded using modify.dkim multiple times).

It can make a PR which removes these mentions, but it would be good to also add a note that require_sender_match used to exist but was replaced with check.authorize_sender at version x.y.z. I'm not sure how to word that properly – I'm just starting to explore maddy.