Package: emacs,gnus Version: 27 When I send email from Thunderbird with a patch attachment, Thunderbird puts something like the following into the email:   --------------AA6C74B60F40E0D600CCD03A   Content-Type: text/x-patch;    name="0001-Fix-decode-time-encode-time-roundtrip-on-macOS.patch"   Content-Transfer-Encoding: 8bit   Content-Disposition: attachment;    filename*0="0001-Fix-decode-time-encode-time-roundtrip-on-macOS.patch"   From 325f51c84d9ad4d9776784bd324b347ffe4fe51b Mon Sep 17 00:00:00 2001   From: Paul Eggert   Date: Tue, 30 Apr 2019 10:45:48 -0700   Subject: [PATCH] Fix decode-time/encode-time roundtrip on macOS   MIME-Version: 1.0   Content-Type: text/plain; charset=UTF-8   Content-Transfer-Encoding: 8bit   * src/timefns.c (Fencode_time): Ignore DST flag when the zone is   ... The attachment has a text/* media type but it has no charset parameter. The patch itself (output by git format-patch) says its charset is UTF-8. Unfortunately, Gnus doesn't recognize the patch as UTF-8 and so mishandles the non-ASCII characters in the attachment. To reproduce the problem, read this email with Gnus; the full attachment is attached to this email in the Thunderbird way. Although Internet RFC 2046 section 4.1.2 says the default charset for text/* media types is US-ASCII, Internet RFC 6557 section 3 amends this to say that registered text/* media types should require a charset specification (or should say it's not needed because the payload has that info, which obviously doesn't apply here). It later says that if there is a strong reason to have a charset default, the default should be UTF-8. Unfortunately Gnus apparently doesn't default to UTF-8 for such attachments, which means that sending a text/x-patch attachment from Thunderbird to Gnus messes up if the attachment contains non-ASCII characters. This has been causing problems on the Emacs mailing list for years and it bit a correspondent of mine again today; see . I have filed a Thunderbird bug report for this, as Thunderbird should specify a charset; see . However, Gnus should be a polite citizen and handle these attachments nicely rather than converting the non-ASCII UTF-8 characters to mojibake.