On Friday,  6 Oct 2017 at 15:52, Robert Pluim wrote:

[...]

> I have my posting styles insert an X-Message-SMTP-Method header in the
> draft which encodes the desired destination smtp server, that should
> survive deferring (although I don't use the agent).

Thank you very much!  This does the job.
-- 
: Eric S Fraga
: in Emacs 27.0.50 + Gnus v5.13 + evil-git-2a918c4
: BBDB version 3.1.2 (2017-01-30 14:47:26+00:00)