From yesterday, my mail server(linux) is not accepting connctions on port 25, I can't send out anything from client mail programs. Please Help!!!

the error information:
Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Account: 'x.x.x.x', Server: 'x.x.x.x', Protocol: SMTP, Port: 25, Secure(SSL): No, Error Number: 0x800CCC0F

And today, the mail server can't receive any email. But if I send mail on internet site, it's ok! Why?

can you send mail from the linux box. See if you can still send mail from the linux box with pine. Just go to a prompt and type pine

How are you accessing your mail server, from Linux or with a Windows client system? A windows client will give the error code you mentioned before if it can not resolve the IP address of the mail server. Also are you using Sendmail as your mail server? If you are using sendmail it tends to be pain sometimes when you have TCP/IP network problems. Have you restarted your mail program to see if that fixed the problem? Along with doing a network & named restart to ensure that sendmail can find itself.

Later

milski

thank you for ur help.

Our network is consist of several laptop with win98, winme. We have four four server, two are NT, mail server and firewall are Linux. mail server uses Qmail. I restarted all services, problems are still there.

what can I do?

Can you still telnet to port 25 from one of the windows clients? What do the log files tell you when you try to connect to the mailserver?

telnet 110 success, but telnet 25 failed, the log file shows:
sysquery: findnd error (NXDOMAIN) AT .....

Well if you can't connect to port 25 then sendmail is not running properly. The error has to do with dns. NXDOMAIN means no such domain. Is the mailserver able to resolve all of it's dns names properly?
I really never configured sendmail so I wouldn't know anything about that, but I assume you've checked all that to so it's sending and receiving it's mail from the right locations.

Mik is right, something is screwy with your DNS services. Look in all your system logs to trace down where DNS is having problems(restart DNS if you must).