The discussion addresses a bug where the reply-key variable doesn’t expand in email custom headers, causing issues for Thunderbird users replying to Discourse notifications. Flominator highlights the problem, linking to a related thread. Sam seeks input from zogstrip, who suggests removing the List-Post header, which is no longer needed and causes issues. nbianca confirms the List-Post header has been removed and that %{replace_key} will now be replaced in custom headers. Flominator reports that the fix resolves the issue, even without custom headers.
We removed the List-Post email header and will replace %{replace_key} in custom headers too. Can you please update and check if it solves your problems?
This one I managed to test last evening and it looks good. The other one I will hopefully be able to test this evening or during the weekend. Thank you!