Subject: bug#56906: 28.1; attachment names containing Chinese characters are handled wrong by default

From: Lars Ingebrigtsen <[email-masked]>
Date: Thu, 04 Aug 2022 08:44:34 +0200

Lin Jian <[email-masked]> writes:

> 3. M-x compose-mail <RET>
> 4. fill "To:" and "Subject:"
> 5. attach a file with Chinese characters in its name, e.g. "测试123abc.tar"
>   5.1. M-x mml-attach-file <RET>
>   5.2. Attach file: /path/to/测试123abc.tar <RET>
>   5.3. Content type (default archive/tar): <RET>
>   5.4. One line description: <RET>
>   5.5. Disposition (default attachment): <RET>
> 6. M-x message-send-and-exit <RET>
> 7. check the raw email on the receiver's side and find this:
>
> Content-Disposition: attachment;
>  =?us-ascii?Q?filename=3D=22=3D=3Futf-8=3FB=3F5rWL6K+VMTIzYWJjLnRhcg=3D=3D?=
>  =?us-ascii?Q?=3F=3D=22?=

I'm unable to reproduce this.  I get:

Content-Disposition: attachment; filename="=?utf-8?B?5rWL6K+VMTIzYWJjLnR4dA==?="

It looks to me like something has double-encoded the header, so probably
an SMTP server somewhere that's mishandling the mail?