I use Verizon DSL service. I have tried to setup a mailserver, but have failed so far. My expertise with linux is rather limited. Hope someone can help.

1) Postfix is installed, and configured (ok I think)
2) If I do "telnet localhost 25" -- I get proper response. But if I do
"telnet ipaddress 25" it just dies without a response.
3) I am able to send out mail successfully

for example, mail xyz@yahoo.com works
4) However, if I mail back xyz@aname.dnsalias.org from xyz@yahoo.com -- I get a
error after a day that SMTP connection was not estblished.

5) I have verified with or without shorewall running, and port 25 is allowed
6) I have allowed port 25 on my linksys router also.
7) I do have a DSL modem, but it is all in default configuration
8) I can repeat step 2, from another computer on the local network.

telent 10.10.10.161 25 works from a windows xp machine.

Any clues? Is it that Verizon is blocking my incoming 25 port? Or is it a problem with DYNDNS settings ( I dont have a dedicated DNS).

Thanks

Usually people will tell you not to use telnet at all, but ssh. Apparently it's very insecure. If you can't receive mail it's probably due to your postfix configuration. Or it may be your firewall. Are you certain it's off when you've tried? Are any outgoing ports closed?

You could try going to grc.com to check which ports it finds open/closed. Shields Up.