How to make a mail sender application approved as secure by Gmail?

I develop an application which has to send emails (by JavaMail) through an external mail server, which can be Gmail too. First I faced a credentinal error, but it came out that cause of the problem was that Gmail refuses the connection from a less secure application by default. When I enabled this option, the connection worked.

My question is: what should I do to let Google accept the application as a secure one? My goal is to use the program without setting of the "allow insecure applications" option in.

Is there a validation process at Google to accept an applicaton as secure? If not, what I need to implement in the sw to meet the requirements?

I've found similar question, but there was only one answer with a guess, instead of a proved solution.

Thank you in advance.

https://stackoverflow.com/questions/67051502/how-to-make-a-mail-sender-application-approved-as-secure-by-gmail April 12, 2021 at 08:56AM