telnet:25 on the right DNS entry ???

[Cricket Liu]

> example: myemail at usa.net
> I tried randomly until I found that to use telnet on the port 25(smtp) the
> right address is NOT usa.net but it is mail.usa.net instead...
> how should a software understand it????
>
> again: it I do telnet usa.net 25 IT WON'T WORK !!!
> I manually guessed mail.usa.net 25 and it's fine but the PC does now
> guess...
> what C/C++ function returns or redirects to the right DNS entry ???

Mail is routed primarily according to MX records for the
destination, and usa.net's MX records don't point to usa.net:

$ dig mx usa.net.

; <<>> DiG 8.2 <<>> mx usa.net.
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 3
;; QUERY SECTION:
;;      usa.net, type = MX, class = IN

;; ANSWER SECTION:
usa.net.                20M IN MX       10 mxpool01.netaddress.usa.net.

So you're supposed to send mail addressed to usa.net to
mxpool01.netaddress.usa.net (at least right now).

cricket

Acme Byte & Wire
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