--On Dienstag, März 22, 2005 13:10:34 +0100 Frank Ellermann
I've given mx 1 because the MTA needs to look this up anyway
For a MAIL FROM nobody(_at_)xyzzy you'd normally not check the MX,
or are you talking about MTAs trying some call back methods ?
Of course you do - unless you are willing to accept mail from senders that
you may not be able to send an DSN to. MX checking is done by default in
most MTAs AFAIK. So the additional cost of a naked MX (as opposed to
"mx:DOMAIN.example") is zero.