Sending Activation Email , SMTP server did not accept the password

I was facing same issue. in my case Password was not so strong. It contains username in password. I change the password and try again. it works. *The other thing you can do that you can use other email address with strong password. make sure captcha is and less secure is enabled. *

https://accounts.google.com/b/0/DisplayUnlockCaptcha

Make sure that the field in 'username' => and 'password'=> is authenticate or valid. I had experienced the same issue and all I do is to go this link https://accounts.google.com/b/0/DisplayUnlockCaptcha and click the button 'Continue'. make sure you're logged in in gmail using the 'username' and 'password' provided in your code. After that, try to send email again.

You need to allow "less secure" apps in your Google account settings:

https://www.google.com/settings/security/lesssecureapps

See this announcement as well http://googleonlinesecurity.blogspot.de/2014/04/new-security-measures-will-affect-older.html

You should implement OAuth2 instead of weakening the security!