On 14 February 2019 08:49 Norman Walsh, wrote:

> Hello world,
>
> I use nnmail-split-fancy to route incoming mail to any of a few dozen
> (or more) folders. Very occasionally, and with no discernable pattern,
> I find a message in the wrong folder. (I have no idea how often this
> actually happens, but I only notice very occasionally.)
>
> So, for example, I find a message in “acmecorp.sales” that’s clearly
> part of a thread that I’ve been reading in “acmecorp.mac-users” (in
> this case). I type “B q” and Gnus (v5.13 btw) says:
>
>   This message would go to archive.2019-02, acmecorp.mac-users
>
> Yeah. Except, it didn’t. It want to “acmecorp.sales”.
>
> Any clue how to debug this?

Just a hunch, perhaps you want to check nnmail-mail-splitting-decodes

I have

(setq nnmail-mail-splitting-decodes t)