Telnet/SMTP only from certain domains

[pcarver]

I have a computer running without a domain name, on IP address x.x.x.x. qmail is running on it. Everything seemed ok...I was sending and receiving fine from a third-party ISP. I dialed into another ISP to test. I am still able to perform pop3 stuff to x.x.x.x (receive mail), but I can't smtp (send mail).

So, it turns out that using the first ISP, I can do a telnet x.x.x.x 25 fine, but when I telnet from the second ISP, that telnet fails with unreachable host.

I can ping x.x.x.x from both ISPs. Why can't I get to port 25 using the second ISP. I know qmail has a few ways to limit which incoming domain IPs, but I think I've got that covered withing my /etc/tcp.smtp file.

Anyone have an idea?

/paul

 

[ifincham]

Hi,

It could be that the 'other' isp uses DUL to prevent spam / relaying. In such cases your have to configure your smtp server (qmail in your case) to masquerade as the smtp server of the ISP, i.e. the smtp server you would configure if you didn't have your own smtp server active or would use in a windows config. See -->

http://mail-abuse.org/dul/gateways.htm#qmail

. Also

http://mail-abuse.org/dul/

for general info on this.

Regards

 

[pcarver]

Hum, I don't think so. I use the term ISP pretty loosely. Both "ISP" locations are pretty much just providing me connectivity. I simply have my own IP address from them. I don't use their mail and nothing on my computer (residing in the ISP) knows anything about their network or smtp stuff.

It's just very strange. I don't think it has anything to do with mail at all.

 

[marsd]

if you cannot get into their smtp port via standard service
reference (25/tcp) it is entirely possible that:

a) you are looking at the wrong server for their mail.
do a nslookup against the isp domain name with the
set type=MX option and record the names of their mail
and try these instead.
Then run telnet or netcat against the isps mail server.

b) they are using (non-standard ports/redirects/masq/acls)
You might want to call them and ask them why they put
themselves through the nightmare of this, as if mail
isn't complicated enough.

c) their mail server is /.

Good luck.

 

[ifincham]

Hi,

Actually I didn't read your first post closely enough.... If you can't telnet to port 25 then its either a routing or firewalling problem. Some ISPs block port 25 except from their own smtp servers - incl. mindspring allegedly.

Regards