In den Release Notes für mutt 2.2 gibt Kevin McCarthy nicht nur seinen Rückzug aus der Maintainer-Rolle bekannt, sondern auch eine kopernikanische Wende im Projekt:
$rfc2047_parameters enabled by default
If you've ever looked at the raw headers of an email and seen text like =?iso-8859-1?q?blah=20blah=20blah?=, that is RFC2047 encoding. It is used to encode non-ascii text in an email header, but has specific rules about where it can be used.
One of the places it shouldn't be used is for attachment names (usually stored inside Content-Disposition:, although historically it could be in other places.) RFC2231 encoding was created for that purpose.
Unfortunately, even though it's explicitly listed as prohibited by the RFC, a few mail clients still do so. You've seen this if you tried to save an attachment and saw a name like the one above.
Mutt has had $rfc2047_parameters for a long time to deal with the problem, but it was set off by default, because.... the behavior was prohibited. However, because the option name is fairly obsure, this often left users (even technically proficient ones) confused and blaming Mutt. So starting this release, I've turned it on by default.
I guess there may be a tiny chance someone wants to send an attachment named =?iso-8859-1?q?blah=20blah=20blah?=, but I think that's much less likely than normal users encountering the incorrect encoding.
Offenbar war ich einer der letzten Menschen, die den Parameter $rfc2047_parameters selbst auf den einzig sinnvollen Wert (yes) setzen mussten.