Re: smtp authentication (sendmail relay)

[Lloyd Zusman <ljz@asfast.com>]

Harry Putnam <reader@newsguy.com> writes:

> Lloyd Zusman <ljz@asfast.com> writes:
> 
> >  Script started on Sun Dec 17 16:16:46 2000
> >  1> telnet smtp.newsguy.com 25
> >  Trying 209.155.56.71...
> >  Connected to smtp.newsguy.com.
> >  Escape character is '^]'.
> >  220 newsguy.com ESMTP Sendmail 8.11.0/8.9.1; Sun, 17 Dec 2000 13:14:33 -0800 (PST)
> >  ehlo asfast.com
> 
> [...]
> Ekkkk.   I'll be damned:
>   bsd > telnet smtp.newsguy.com 25
>   Trying 209.155.56.71...
>   telnet: connect to address 209.155.56.71: Connection refused
>   telnet: Unable to connect to remote host
>   reader@satellite /anex/reader
> bsd > date
> Sun Dec 17 14:01:54 PST 2000
> 
> 
> And... Newsguy tech staff have told me over the phone that  telnet is not
> allowed.
> 
> Not sure what the deal is now.

Well, the only thing I can think of is reverse DNS.  Many servers
don't allow connection to them unless the connecting host's IP address
has a valid reverse DNS entry.  The IP address of machine from which I
was connecting indeed does have a valid reverse DNS entry, and so
perhaps this is why my connection works.

In case you don't know what "reverse DNS" is, it's a function of DNS
service which will return your domain name when your IP address is fed
to it.  Normal, "forward" DNS goes in the opposite direction: it
returns an IP address when a domain name is supplied.

The people who supply your IP (i.e., your ISP) are responsible for
supplying reverse DNS for your IP address.  Ask your ISP if this can
be enabled.  It's extremely common these days for ISP's to provide
reverse DNS, because for security reasons, most servers on the net
(SMTP, NNTP, telnetd, ftpd, etc. etc. etc.) are requiring valid
reverse DNS from those who connect to them.

If your ISP won't supply this service, I regrettably must suggest that
you switch ISP's.  And by the way, if your ISP says that reverse DNS
isn't possible with dynamic IP's, this isn't true, since many, many
ISP's routinely supply proper reverse DNS entries for their dynamic IP
customers.

HTH

-- 
 Lloyd Zusman
 ljz@asfast.com