spam filters rejecting emails

Many of our emails are either going to SPAM or are getting rejected by SPAM filters with a message of Sender IP 550 Address is blacklisted,  I checked mx toolbox and received some warning messages such as Reverse DNS does not contain hostname and Reverse DNS does not match SMTP banner, but were not blacklisted on their free listings.  Any suggestions on how to correct these problems. We are blacklisted on justspam.org and SPAMCOP.