Message like this (example is heavily redacted): User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 Content-Language: en-GB-large Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable Ahoj, =C2=A0 p=C5=99idal jsem kluky explicitn=C4=9B do CC, je=C5=A1t=C4=9B p=C5= =99id=C3=A1m tebe do jednoho=20 ticketu co m=C3=A1m otev=C5=99en=C3=BD. Podle m=C4=9B je to po=C5=99=C3=A1d= jeden a ten sam=C3=BD probl=C3=A9m s=20 SSO. M. will be decoded like this: Ahoj, __ p__idal jsem kluky explicitn__ do CC, je__t__ p_ _id__m tebe do jednoho ticketu co m__m otev__en__. Podle m__ je to po____d jeden a ten samý problém s SSO. M. I.e., just the last line of the main paragraph is decoded correctly. This is claws-mail-3.17.4-3.fc30.x86_64 on Fedora 30. View -> Encoding and View -> Decode are both set to automatic. I tried to paste the raw text to several online decoders and it was decoded correctly.
*** This bug has been marked as a duplicate of bug 4224 ***
> *** This bug has been marked as a duplicate of bug 4224 *** Are you sure? The other bug is (according to comments) caused by HTML-to-text parser, but this use case is about plain text messages; there's no HTML involved at all.
Hmm, now you mention it, no, I'm not sure. I'll re-open until there is more time to evaluate.