I found an interesting recent thread among Apple people, OS X, the
getaddrinfo() issue, telnet applets acting with MTA-like behavior, and
also the debate of the meaning MX records:
http://episteme.arstechnica.com/eve/forums/a/tpc/f/8300945231/m/619001401931/p/1
Apparently, the OP did a direct telnet connection on port 25 and the
telnet application produced net packets with MX lookups apparently
because the application is using getaddrinfo() function.
As the original poster said in the thread:
If I want MTA behaviour I'll use an MTA. telnet and nc are
not MTAs.
Yes, they're used for diagnosing problems with an SMTP server,
which is precisely why they should let me connect to the SMTP
server I'm trying to diagnose, not play silly buggers with DNS.
The scary thing about all this is how lower layers is forcing the
explicit MX issue.
Especially with this dude saying this on page 2 of the thread:
I also think your notion that telnet/nc to port 25 should
ignore ESMTP rules is equally silly (or at least, have no way
to be made to follow them): if I'm at the point where I want to
send SMTP commands by hand, I'm also at the point where
assuming that DNS lookups are working right is a bad idea.
This would be true if TELNET was going to fully act as MTA and perform
the state machine exchange.
Go nuts.
--
Sincerely
Hector Santos, CTO
http://www.santronics.com
http://santronics.blogspot.com