RE: sender_agents modifier

The biggest problem with this is that most domains won't have enough
information to reasonably set "sender_agents".  Clearly, if your domain
permits people to send personal e-mail, it can't possibly know.  (It
doesn't know whether I have a Blackberry or equivalent, for example.)

However, I suspect that this inability to set "sender_agents" reasonably
won't prevent many domain owners from setting it unreasonably.
Therefore, I don't think it's a good idea.

-- jimbo