550 Unrouteable address

Hi,

Internal mail works between different accounts.

But, when using external email service providers to send mail I get 550 Unrouteable address error.

TinyCP:  

user1@mydomain.com -> user2@mydomain.com - ok

user1@mydomain.com -> someone@gmail.com - ok

someone@gmail.com -> user2@mydomain.com - nok

What's going on?

This kinda helped

Settings and testing are hidden here for email debugging:

This server > Web > Domains > Domain: (yourdomain.com) > Emails