As of May 30, 2022, Google has required OAuth authorization for Gmail accounts, and while ordinary SMTP (a.k.a. "Less Secure App access) is still possible with Google Workspace (formerly GSuite) accounts, they have indicated that they will be turning this off in the future as well.
This has been recognized in the Drupal version(s) of this module, and there are currently issues and patches for both D7 and D8:
As of May 30, 2022, Google has required OAuth authorization for Gmail accounts, and while ordinary SMTP (a.k.a. "Less Secure App access) is still possible with Google Workspace (formerly GSuite) accounts, they have indicated that they will be turning this off in the future as well.
This has been recognized in the Drupal version(s) of this module, and there are currently issues and patches for both D7 and D8:
Drupal 7 issue Drupal 8 issue
In both cases, the submitted patches create a new submodule,
smtp_oauth, that provides OAuth authentication.I have ported the D7 patch to this Backdrop module. PR to follow shortly.