Use gvim in kmail
From Vim Tips Wiki
created August 7, 2002 · complexity basic · author Davide Patti · version 6.0
To automatically open gvim to edit in kmail, "-f" command line option must be used.
In kmail configuration go to the composer settings, and write in the "use external editor" field the following command:
gvim -f %f
Without -f option gvim would work in background and editing would not have any effect on kmail.
To set the filetype automatically to mail:
gvim "+set ft=mail" -f %f
See also http://freehackers.org/kvim/ - integrating Vim in KDE. It looks really nice! (I'm not sure of exactly what is needed to get it running i KMail though - but look at those nice screenshots..)
-> kvim changed its name to yzis, so have a look at http://www.yzis.org/
This tip is basically true for every mua that allows integration of external editors, e.g. mutt
Yes it works also with kvim (which is the KDE way). Just put "kvim -f %f" and you're done, when you start typing, it fires up kvim, when leave with :x you get back to kmail kinda like when you use vim with pine.