Excerpts from Gaute Hope's message of Tue Mar 09 11:29:13 +0100 2010:
> Could someone be so kind and provide an example for setting it to i.e.
> 'Sign' by default, given a specific from address?
> 
> - gaute

Something like this should work:

crypto_selector.set_to :sign if header["From"] == "foo@ba.r"

(You might need to use e.g. a regex if the header also contains the name,
as in "Foo Bar <mail>")