ISSUE WITH UNABLE TO SENT OR RECEIVE MAILS
1, Check mail service is up or not /etc/init.d/exim status
2, Check by send a test mail from test mail a/c, tail -f /var/log/main_log (For dynamic checking )
3, Check the Ip listed in RBL (Search the key word 'spam database' in Google)
4, check by disabling the firewall , as it may be blocking the port 25
5, check it by telnet to 25
6, Check the error by sending a test mail from the account,
if you are getting any error regarding MX priority check the domain is listed
/etc/localdomains (if the domain is using the server MX) or
/etc/remotedomains(if the domain is using remote server MX)