A client website recently has moved to a new server and the Drupal PHPMailer module failed to authenticate the Gmail account. You could try the following steps to allow other application to access your account.
1. Go to https://accounts.google.com/DisplayUnlockCaptcha and click Continue.
Continue reading GMail authentication problem in PHPMailer
If you want to send HTML email using the PHP mail(), here is an example.
Continue reading PHP – Send HTML Email
Setting up Sendmail to relay public SMTP server such as Gmail is quite difficult. In the past, i just kept looking for the blog posts in Google and found that people have different ways to setup Sendmail, but not all of them could be repeated successfully in my setup. After so many trials and errors, i made the relay works but i couldn’t fully understand what’s going on in the setup.
So this time, no more Sendmail, i would like to use Postfix instead. Continue reading Postfix – Relay via Gmail