I host a server on Google Cloud with Protonmail Bridge running in the background. I am still new at working with CiviCRM 5.26.1 and PHP. I can successfully send emails via Drupal usinig the SMTP module but with CiviCRM I receive this error when I send a test email:
authentication failure [SMTP: STARTTLS failed (code: 220, response: Ready to start TLS)]
In the Bridge Configuration Guide, an exception has to be set on Thunderbird.
Now, according to this solution that would seem to solve my problem : SMTP connection failing problem, I don't have the same structure when I open the /Net/SMTP.php file.
Note: This exception is needed for Protonmail Bridge.