Fixing 'Call to Undefined Function' Filter_Var() in PHP

I host a lot of websites in the Amazon cloud on EC2. I recently discovered that all email one site was sending was being rated as spam and never seen by the recipient. This meant that new users didn't get the verification email required to complete signup. It appears that EC2 IP addresses can have a dodgy reputation among email providers. Another web publisher described these problems on AWS Developer Forums. Since then I've been rewriting my code to deliver emails with SendGrid, a service ... (read more)