The email sent from my server are marked as spam

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http://serverfault.com – I have a dedicated server at OVH. For several days I've noticed I'm in a spam list (spamcannibal). The reason I said was for generic PTR. I've changed and I have commanded to remove from the list. I've been reading about the steps to configure the dns well but I did not clarify. I have 3 domains hosted on my server and send emails 3. if I type host [my ip] servidor.mydomain.com me back and if I type host [servidor.mydomain.com] return my ip Is this correct? mydomain.com is one of the three that I have hosted (HowTos)