🇫🇷France @deajan

I stumbled into that issue also.
Having installed modules via `composer require drupal/smtp` and `composer require phpmailer/phpmailer`, I still got that error message.

After a bit of search, I noticed that the permissions for my phpmailer folder were wrong (no webserver permissions).

Anyway, after I changed the permissions with `chmod -R apache:apache vendor/phpmailer`, I still got the error message, but basically it should work at this step.
Rebooting php and httpd finally got rid of the error message.