[Skunkworks] Blacklisted mail servers

Hi guys, I've been receiving complaints lately from my users about messages not getting to them and on investigating, I have found that a number of local ISPs have blacklisted mail servers. Is it just me or is it common among admins on the list? I have configured my mail server to reject messages relayed by mailservers blacklisted by spamcop, spamhaus and barracuda and respond with a message explaining that action. Now this has got me wondering whether I have made my security settings too tight or what... Is that too drastic a security measure that I have taken? Me.