I have problem with SMTP.
On the same server as the SMTP account it works, but when I enter the server address as localhost.
But when I connect to another WordPress on another server with SMTP mail.domain.com, this error:
SMTP connect() failed. Troubleshooting · PHPMailer/PHPMailer Wiki · GitHub
But when I test by online testers from google, it works. I don’t understand why that is.