E-mail notifications are the lifeblood of social networking websites. The proliferation of spam email and authorities that monitor servers sending spam is a seemingly never ending battle. Because spam’s increasing prevalence, sending email with “quality” headers is absolutely essential to successful delivery.

I recently worked on an issue with a custom built notification system sending emails and sms messages after certain events. Some of the e-mail messages were delivering successfully and others were not. Review of the code revealed the usage of drupal_mail_send, with improperly built custom headers, was causing the emails to deliver incorrectly.