CSF :
my email server being black listed, for sure i can not send email to people but
people still can send email to us?
Blacklists are unidirectional. They are used by receiving mail servers to determine if the mail server sending the mail is a well known source of spam or maliciousness. They do not prevent a mail server that is on a blacklist from receiving mail, though that mail server itself may check the sender against blacklists.
If you inherited the mail server's IP from someone you can look it up on public blacklists to see if it's been marked, although public blacklists are sometimes hard to get removed from. Private blacklists cannot be searched but will sometimes autoreply to the sender or domain postmaster notifying them...