qmail-smtp

[edy]

i dont know that i in right list to post this problem, but i have a problem with my mail server using qmail and under operating system redhat 7.1. the problem in several days like 2 day my mail server have a problem with smtp, the clients cant send mail and the error message from the server is server dont response. and the solution that i do know is restart the mail server.   any body can help me what should i check and do to fix this problem???     thanksss