"Sven Bretfeld" <sven.bretfeld@gmx.ch> writes:

> Since I use my imap account not only with Gnus but also with K9
> (Android) I have some problems with the expired-mark. As far as I can
> see, non-Gnus clients cannot set an Email as expired, can they?
>
> Therefore, I have several messages in my inboxes marked with "O" (old),
> which excludes them from the expiry-process. Back in Gnus I have to
> manually set them to expired with by hitting "E" one after the other. 

Not what you asked, but I do this totally differently.

I use gnus as my main mail reader, and also thunderbird, osx/Mail.app,
and iphone/Mail.  While my mailinglist mail is like news, I consider my
INBOX to be not like news, and basically only want to explicitly delete
things.

So, I have all the non-gnus MUAs set up to delete by moving to
nnimap+[foo]:Trash (vs "Deleted Messages" with whitespace), and then

Then I bind 'd' to

(defun gdt-gnus-move-to-trash ()
  (interactive)
  (gnus-summary-move-article nil gdt-trash-newsgroup))

and delete messages when I'm done with them.

This works for me because I filter (before delivery, not with gnus)
messages that aren't more or less to me personally to one of about 100
other IMAP folders.  Most of those I both set auto-expire=t and read
only with gnus - basically they contain (by construction) data that does
not require timely processing.

This whole scheme is built around the notion that I want reading the
INBOX on my phone to be useful, which for me means that all mailinglist
mail (and anything that gets even 1 point with spamassassin) does not
go to INBOX.

I suppose you could write something that finds messages marked read but
not expirable in groups that are marked auto-expire.