SMTP Connection Refused

[Ki Song]

I am running Fedora Core 4 using Postfix as my mail server.

When I send/receive e-mail messages from an outside client (yahoomail,
gmail, hotmail, etc.), the messages are delivered properly.

However, when I send a message to a different e-mail server in house
(store.knifecenter.com), it says the connection is refused. Here is the
exact message that is returned in the postfix maillog:

connect to store.knifecenter.com[70.88.225.6]: Connection refused (port 25)
D7C9C3572A1: to=<listserv at store.knifecenter.com>, relay=none, delay=0,
status=deferred (connect to store.knifecenter.com[70.88.225.6]: Connection
refused)
disconnect from unknown[10.1.10.19]

What is going on? Any ideas?