Mailing via Gmail SMTP in Joomla gives error message

When you want to mail in Joomla via Gmail/Google's SMTP, you may get a message "Could not authenticate".

There is a good chance that you have recently enabled two-step verification in Google.
Supposing you have checked all the settings for the mailing in Joomla via SMTP, the solution in this case is to create a so-called Application Password (App password) in Gmail.

Creating App password is explained in this instruction.

The password you obtain with this should be set in the smtp data in your Joomla site.

Always click the button at the bottom to send a test mail.