solution was very simple: disable the Luser relay command. My friend who helped me setup the mail system was having a hard time, so he activated it. This way it was guaranteed that ALL mails will go to the system, even if there were no users. And I never checked the system.
This morning I found out that he was having a hard time because he had put @haitiwebs.com instead of haitiwebs.com, so the system could not receive emails, making him to use Lrelay user.
Once I remove that @ mail was fine and lrelay could be disabled. Now we only get emails for legitimate users. As a result, resources are preserved and everything, including posting is faster.
Have been busy lately, so did not have much time to spend here.