I've been having some trouble on one of my drupal sites for the last weeks, first the contact form stopped working Won't send any mails. Then all mail sent from my site stopped working and i just keep getting the error message "Unable to send e-mail. Contact the site administrator if the problem persists."
I've searched around for a solution but can't find anything on how to solve this. I'm using a email address with the same domain name as my site.