How to make a reliable application for accessing a Google account?

Question

Google

Greetings!
I write PHP online tools for sending emails to clients.
The mailing is done by the manager.
Each manager has his own mailbox on GMAIL, SMTP of his mailbox is used to send letters.
Problem : When you send a letter for the first time, a letter arrives,

then you need to enable the option

and then you can continue sending letters, but after about 30 letters, the account is blocked for security reasons, and you need to change the password. Blocked due to the fact that my script suspects illegal actions in relation to my mailbox.
How to allow untrusted apps to access your account
Which states trusted and untrusted apps.
How can I make my app trusted by Google?

Answer 1

Most likely, you need to add support for SSL / TLS, and the latest versions and prohibit the use of obsolete protocols.

Answer 2

You need to mark the application you use (your php script that authorizes) as reliable in the settings of each Google account. In my opinion, this can be done directly from the link from the notification letter "View the list of devices."
After that, no questions will be asked.