It would be useful if one could set the default sender address to use when
sending mail to a particular contact.

For example, I have business contacts to whom I should always send mail
from my business address and personal contacts with whom I prefer to use my
personal address.  It would be nice if I could set this in the contact
information so evolution made the change automatically when the address is
added.

This may not be possible in terms of the mailer.  I imagine conflicts could
arise when sending to two contacts with different default addresses.  But
that would not be the usual case.  Perhaps some solution could be found?

Of course, it would be necessary for the user to be able to override this,
but it would be convenient as users often forget to reset the sending
address from their default address.