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Re: detect ISP's legitimate SMTP server
From: "RPLists" <lists () reversepath net>
Date: Thu, 3 Mar 2011 16:46:25 -0600

I was abroad in Germany with my Nokia n900 and I needed to send few
emails over the HSDPA connection. The problem was, that I had no idea
about ISP's SMTP server and the one I use in my country did not
work(most likely ISP allows to use only the legitimate ones). I
detected the ISP using the IP address and whois information about it
and finally gave them a call. However, is there some sort of smart way
to detect legitimate SMTP servers in ISP network?


Some ISPs may not allow you to use their outgoing SMTP server unless you
are a customer of said ISP. These days, ISPs should implement SMTP AUTH or
TLS etc.. however, that is beyond the scope of what you are requesting.

Provided you have a unix/linux box available to you, you can issue 'dig -x
a.b.c.d' to find the reverse DNS record for the IP. This will give you the
host and domain name associated with the IP (if the the in-addr.arpa
record is present). If you already have the information via WHOIS you may
have domain name information handy. You can look up the mail exchangers or
SMTP servers using 'dig MX domain.com @<dns.server>'  or even try to query
dig smtp.domain.com.

You can even issue nslookup commands from a DOS command prompt and do
nearly the same thing.

If you do not have access to a unix/linux box or windows DOS prompt you
can use the "Domain Dossier" at centralops.net (http://centralops.net/)
and it will spit any useful information out for you.



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