When sending PGP/Inline encrypted messages in Claws Mail, it uses: Content-Transfer-Encoding: binary However, RFC2045, section 6.2. Content-Transfer-Encodings Semantics, https://tools.ietf.org/html/rfc2045#section-6.2 , specifies that "[...] there are no circumstances in which the "binary" Content-Transfer-Encoding is actually valid in Internet mail." This section is further updated in rfc6532, which still does not permit to use binary content transfer encoding in the way it is currently done in claws (it would require using message/global instead of message/rfc822).
The claim in the summary is untrue. Also you're misquoting, quoting out of context, and/or mis-reading the RFCs.
In fact, it does, maybe not always but it does: Date: Fri, 19 Jul 2013 09:39:17 +0200 From: Colin Leroy <colin@colino.net> To: colin@colino.net <colin@colino.net> Subject: test Message-ID: <20130719093917.4bf4032d@colin> X-Mailer: Claws Mail 3.9.1-20-g937596-dirty (GTK+ 2.24.13; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: binary -----BEGIN PGP MESSAGE----- Version: GnuPG v1.4.12 (GNU/Linux) hQEOAyeRXT2msRnlEAP/aKrdV4opuM9Vt785IU/EYeOazXJdila+DmVvzlu+Cn2T bmCD0z6ymAv+0Yt9kIIrflEqY4yN/hOTeorUiNAxMqI/d2OAbl3WIUUytGI02UlB WIul15brBnxDP/rdYovgh/3Yx2GxpC3RGX/gz5HMec3iyT7lmeCa+VRCQ3nz4qwD /jHaG7fu/kUe4Y/39fOychRm2HRE/nyenD3xUQ5HkK+ZQIBrZh6FsnbtGFg3wvvi Lv9AIU0a/ZC600nfnkgs4iFCcg1h7OgWNRO9vP2mEpxlf866ocsSZrmgTvwoLEVx l/hsoBdWxVlB4CfmOoPqJTRVTHy6QOd+T/gHUBdMOVzH0o0B/xsPsBuUeWXz9Ytf y1ywJyBg2icai6KD2ELFP4qaqp/9KkVhsuD+nCjkF+cHO4lFCTIh7J7oPUR3H7X9 /SyDAmrbeUgmYxZMtCqmKYbVlKDKaEZh/zlExxP2//nNH7FtQ4RlOak6NmVZhotW eD2pE819qkg9UCuMbs39IUHIjvaBXNw7pUk6GELOa/w= =YIi8 -----END PGP MESSAGE----- But I fail to see how this is a problem...
Date: Fri, 19 Jul 2013 08:08:29 +0100 From: paul@claws-mail.org To: paul@claws-mail.org Subject: test Message-ID: <20130719080829.62fe24a5@claws-mail> X-Mailer: Claws Mail 3.9.2-31-g50116e (GTK+ 2.24.17; i686-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit -----BEGIN PGP MESSAGE----- Version: GnuPG v1.4.12 (GNU/Linux) hQIOA7Tgv+8phhjWEAf/fs9fbj06fEwPyHW313erdy+czy9WCiJB66SUcsfjfyAe Kks2pBCIk8a1FvQi9C4fKOhFSpoIgT3ztIh1AgFK8QjFBRV//KOPnjgInQVeKXWf +aKadpgJp/KhVHWf+D+aBW/ovbspCBk0Y+DomKiS8FhXOkMGP2pXIobgLBGT3FPA NiSddJzTXkgtGJf2RXYr8c2018ieU5OLOjCnc2wTBLVJjWoAp6bFioNJ+a/Hn/NC kjO4K04ymKw5fNvfWmcD3sI5pv4CaOYwfWoVG0dOsaPRjH/RTYt1dHG0YIuDJek6 ZAYx3fDNLEEG+qYyJ1nDEwV5dhKf0tS07SyR6IcTIQgAlIrHvGRM8zOZvytWKTm+ F9F2yRIRY8I1IA2d2qmnPLtcGRFQjHdmXFNa191Rqok9KGxym6LUWMKoMR+lOCLR RZz2iJIkNOSE3pPRrFDJxaAaP2Q570JM4qALVnOccRHtZ3h5tNvLs4wMlV4X7ceW PdX4J6Uf8zJIQh5791su1kMA2nEgSC6wcSg7+211/0SSiIZGqRAOYxVWOZfsPwYy e7+YE98B7QWtPJ8Y8ee31CxIXKOknYJiLlhZ0MOrSbQ2CAh+HntmrcZv9Ura4+EB N/nhE973UhZX1AV1qtNbTjwTSM3gO6FBnlQPEA6baG7IEaFHCdxXLommPNRraiPl OtKXATDerkAJq3n93q5sqQujmYuNs0YHDsAUIIleL1t6jgzGpCOhJ6sdZMasXyqm Mjj6OKfH6rlDn24AEuE1C/Thwn6fAx0rICtvDNvcEQCCKOAfZBxdihRU2mab5WJm f8KMCLF9grgaWn6BgbMiTaAwfR/uo813bDl1vGhBdZ3ZLpEiEYKmtxme4gH4QQII 3bbMrz+qKswesA== =yF5v -----END PGP MESSAGE----
Ah, it depends on the locale's default charset, then.