During March 2014 AsrHost discovered one of our websitePanel smartermail server was allowing unauthenticated emails for internal domain emails to successfully be sent.
As a security measure we have fixed this so its got the same correct configuration as our other Smartermail Servers.
You will receive a 550 authentication error if your sending an email from (example) user1@domain.com to user2@domain.com without having SMTP authentication setup in your email client.
You will need to make sure you use SMTP authentication from your email application or web scripts, as if we allowed unauthenticated connections, this would allow spam emails to be sent to your account.
If you send emails from a remote server that does not allow you to setup SMTP authentication, you will need to speak with the developer of your application to implement this feature or have the remote server send from another domain name that is not the one hosted with us.
This will effect a very little percentage of our customers, as most clients will authenticate when sending emails.