Not receiving all notifications

I have this module set up to notify a user via e-mail every time certain node types are created and it's only working sporadically. I'm still in the testing phase of this site but it needs to be deployed fairly soon. I'm the only active user on the site right now so I know I'm not overloading the messaging system; however, I can't count on e-mails being delivered. I'll get a few in a row, then every other one for a while then two in a row will go missing...
There's no rhyme or reason to it.

I've tried with the PHPMailer and simple mail handlers with no change.

Thanks,
David