Is anyone know what is the problem?
I would think it is port 587 is not open for submission
To check, just telnet to your server on port 587. If you cannot access your server on this port, you can do either as follows
Set your port to 25. TLS and upon connection, it will upgrade connection, or open port 587 in firewall.
I hope that helps and sorry if I’m wrong
Sorry, your errors are in red in your picture.
Your username or password is wrong but this may be because your domain cannot be resolved by DNS.
Does your domain exist, or is your DNS running, or are setting the records correctly at NS
I have completed a few little tests based upon your domain is correct as shown in picture.
All you need to do is change smtp.vonline.eu to mail.vonline.eu.
This should work fine for resolution and any failures then would be either your username or password.
I hope that helps