On  2 Jan 2018, Eric S. Fraga wrote:

> Hello,
>
> I use emacs snapshot on Debian.  Recently, but cannot say when
> exactly, my email composition has started behaving strangely with
> respect to auto-fill mode.  Specifically, if I'm responding to an
> email, as I type, long lines get auto-filled with "> " as the prefix.
> The first line of the paragraph does *not* start with "> " and I
> usually have at least one blank line between the paragraph I am typing
> and any included text from the original email.
>
> I have searched my configuration for anything that would affect this
> but I have nothing.  When it comes to auto-fill, I've left everything
> as default as far as I can tell.
>
> Any suggestions on how to track this down would be welcome.  

I'm using Emacs25 and Emacs-Snapshot on Debian. My emacs init loads
'Trivial Cite' (TC), and I do *not* experience this issue.

TC is in Debian's emacs-goodies-el. Perhaps a comparison of TC and the
Emacs efault will turn up a clue.