Automatically find right GPG record when signing/encrypting mail?

[Kai Grossjohann]

I send mail to user foo, but my GPG keyring gives address bar for
this person.  I know that I can specify the recipient in the mml tag,
but is there an automatic way?

(There is perhaps a way to do it with GPG; that would be fine, as
well.  I don't want to use the email address given in the key, as it
is old and will stop to work sooner or later.)

tia,
Kai