There are many different blacklist providers in existence and if spam mails sent from your server then your server ip will be blacklisted in spam monitoring site.

Lookup on any of the following website for checking whether server ip has been blacklisted or not. If its blacklisted by any one of spam monitoring site,then request them to remove ip from their blacklist database by giving removal request in their site. Once its removed from blacklist,then mails wont bounce back to your mail account.

http://multirbl.valli.org/lookup/
http://www.mxtoolbox.com/blacklists.aspx
http://www.blacklistalert.org/
http://www.dnsbl.info/dnsbl-list.php