It will work the same as V4
You will need to prefix your .env with the primary key of the company ie 1
1_MAIL_HOST=
1_MAIL_PORT=
1_MAIL_USERNAME=null
1_MAIL_PASSWORD=null
1_MAIL_ENCRYPTION=null
And for these configuration, always ensure your cache is never optimized, you’ll want to run:
php artisan config:cache
php artisan config:clear