This error means that the sender is trying to send an email to an address which he is not allowed to send to. This message is generated after hMailServer has checked the IP range settings. As an example, the defualt IP range configuration does not allow external users to send messages to other external users. This is to prevent people from using your server to send spam. So if an external user tries to send a message to another external user, he will get this message.
You have enabled SMTP authentication for the IP range that the user is connecting from, but the user has not configured his client to use SMTP authentication. There's two ways to solve this problem. Either configure your email client to use SMTP authentication. This setting is normally found in the account settings in your email client. Or, disable SMTP authentication for the IP range. The first solution is recommended since it reduces the risk that anyone will send spam through your server.
By default, hMailServer does not require SMTP authentication for connections coming from localhost / 127.0.0.1. For connections coming from other hosts, SMTP authentication is required for deliveries to external recipients. By default, hMailServer never requires SMTP authentication for deliveries to local accounts, since that would prevent other e-mail servers to deliver email to your installation. For information on how to enable SMTP authentication, check the HOWTO.
When hMailServer deliver an email to another server, the receiving SMTP server may try to validate that the email sender really exist. If this verification fails, it may respond with the error message 'Sender verification failed'. In these cases, the email will be bounced back to the sender. This verification works the following way:
There are a few things which can go wrong in these steps:
This error message typically indicates a server configuration error. hMailServer does a number of checks before message delivery to prevent infinite message looping. When an email is sent and the recipient can not be found in the local installation, hMailServer will normally try to connect to the recipients email server to deliver the email message.
Before hMailServer connects to the recipients email server, hMailServer checks that the IP it is going to connect to is not a local IP address. If the IP is a local IP address, this would mean that hMailServer would connect to itself, which would likely cause a message loop. In this case, hMailServer rejects the message delivery and returns an error message to the sender instead.
The following causes are common for this problem:
If hMailServer looses the connection to the database server during a query, hMailServer tries to re-open the connection and re-run the query. If this fails, the error MySQL server has gone away is logged. This can happen if the MySQL server is run on another computer, and the network connection is dropped. It can also happen when the MySQL server is about to be stopped, for example just before a computer reboot. In most cases, this failure will not have any side effects.