SMTP Protocol Returned a Transient Error

Hi,

I am encountering a problem with SMTP, for incoming mails from outside.

When a external server tries to connect to my server via SMTP, it gets the following error : “No messages transferred to XXX.COM via SMTP: SMTP Protocol Returned a Transient Error”.

On the other side, it seems that my provider relay servers keep connecting permanently (8 servers, connecting the one after the other), but they try to send me mails that my server rejects for policy reasons, as far as the mail address is not in the domino directory.

Does anybody has ever found a solution to that issue ?

Thanks to all in advance, any idea is welcomed.