I have been using PHPMailer for several months to send email OTP verification and automated alerts from my website using a regular @gmail.com account. This setup has been working flawlessly until last week. Now, all new users who register on my website are not receiving the OTP email for verification. Instead, I receive a “Message Rejected” error, and the emails bounce back to the sending email address.

Let me preface this by saying that I am not trying to use gmail as my smtp server.
I am able to use PHPMailer to send emails to most all addresses from my host (hostgator) using my domains smtp server settings except for sending email to gmail addresses. Email sent to gmail addresses just never arrive. As far as I can tell, I am not getting any error messages.