I would try 2 things first:
I would open a support ticket and ask if there is anything wrong with the server or the outgoing mail queue's. I haven't really seen posts about it lately but there was a time that outgoing mail queues got clogged with spam.
Second, if you have a recent email sent by the script verify it's first (bottom) "received by" header says yourservername.dreamhost.com. then go to this page and put yourservername.dreamhost.com in the search box. (using your own servers name of course =] )
if your server is blacklisted, the quickest remedy is to reconfigure to use smtp to send and use mail.yourdomain.com as the smtp server and the credentials to one of your mail accounts, that will change the outgoing mail server.