Its deeply upsetting that the specification for `mailto:address?in-reply-to=message_id` is [26 years old](https://www.rfc-editor.org/rfc/rfc2368) and yet barely any software supports it besides Thunderbird :-( And the alternative option is downloading an e-mail message file (`.eml`), opening it, and replying to that; but how many people even have desktop e-mail clients setup any more?