In-Reply-To and References headers getting dropped when replying to public mailing list

[suhail-singh]

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When replying to a public mailing list that you're not subscribed to, the
In-Reply-To and References headers are dropped. I believe this is a
recurrence of #374 as noted in comments:

• In-Reply-To header spuriously missing when using git send-email #374 (comment)
• In-Reply-To header spuriously missing when using git send-email #374 (comment)

Expected Behavior

The In-Reply-To and References headers should remain as set by mail client.

Current Behavior

When In-Reply-To and References include message IDs that weren't received in
protonmail inbox, the headers get dropped.

Possible Solution

As noted in this comment some of the checks being done in smtp.go are
unnecessary and too stringent.

Steps to Reproduce

Compose a message with your mail client of choice with an In-Reply-To
containing a message-id that has never been received by your inbox. In the
email that gets sent, the In-Reply-To header is missing. Similarly for
References header.

See also #374.

Version Information

3.9.1

Context (Environment)

I am unable to respond to any public mailing lists that I review via Gmane, nor
am I able to effectively participate in patch submissions using Protonmail.

Detailed Description

The In-Reply-To and References headers should not be altered if set by the
mail client.

Possible Implementation

[LBeernaertProton]

Thanks for the report, Internally tracked as GODT-3297.

[suhail-singh]

@LBeernaertProton you're welcome. If this is, indeed, a recurrence of #374 (GODT-2569), could its resolution also include a test to prevent such regressions in the future?

[suhail-singh]

@LBeernaertProton it's been a few months. Could you please share the internal status of this issue?
Without this resolved, I am unable to use the bridge (or proton mail) for a majority of the emails I send.