[CLUE-Tech] Sending mail using an IP address?

[Jed S. Baer]

Greetings folks.

Maybe I'm confused, or just remembering simpler times.

Due to some dns resolution problems, I tried sending an e-mail directly to
a mail server I identified using a dns mtx query, i.e. theperson at n.n.n.n -
which bounced, because of a host lookup failure at my ISP. Now, I can
understand how it might bounce at the other end, because it might rely on
having the domain name component for identifying the recipient, if the
mailserver is handling multiple domains. But I just don't buy the MTA
being unable to recognize a dotted-quad IP address and using it.

I really don't want to become an SMTP guru, or a sendmail or postfix guru
either. So maybe somebody has nice URL where this is explained, or could
tell whether my ISP is blowing smoke, or whatever. Here's what they said:

< quoth >
All mail is handled by name, not by IP address.  This is an internet-wide
standard that everyone adheres to.  You cannot send email to an IP address
only.  I have talked with our system administrators about this, and I
have done some testing myself, sending to different email addresses at
the mail server's IP address.  I have sent through many different mail
servers and they all have this same problem.  Mail absolutely has to be
handled through DNS, so sending directly to the IP, instead of the name,
is not possible.
< end quoth >

But really, isn't sending mail, well using SMTP anyway, just a matter of
having a server/daemon listing on the proper port, and sending a properly
formed message to it?

TIA.
jed
-- 
"Those who expect to reap the blessings of freedom must, like men,
 undergo the fatigue of supporting it."
 - Thomas Paine