What security can we implement in PHPmailer to make it a more secure app for Gmail? https://support.google.com/accounts/answer/6010255 I am using PHPmailer to send emails via Gmail. PS: I don't want to enable "access for less secure apps" here: https://www.google.com/settings/security/lesssecureapps, I want to make the app more secure.
Gmail has started imposing a new authentication mechanism that substitutes SMTP athentication for OAuth2-based authorisation. The docs on their changes can be found here.
This doens't really improve security much because ultimately you still need to submit your username and password over SSL at some point (the very mechanism that google deems insecure) to authenticate to get an OAuth token, which is exactly as secure as existing SMTP auth systems.
As yet, PHPMailer does not support this new mechanism - PRs welcome! You will need an OAuth2 class, such as this one, and perhaps make use of this code example.
In the mean time, you do have to "enable access for less secure apps", and you should set SMTPSecure = 'tls' and Port = 587 and use normal auth to connect using PHPMailer.
Update
PHPMailer supports Gmail's XOAUTH2 authentication as of version 5.2.11. See this guide. It's being expanded in version 6.0 to support other services too.
来源：https://stackoverflow.com/questions/28125138/make-phpmailer-a-more-secure-app-for-gmail