Can't receive mails from one particular sender

Hello,

I can’t receive mails from one particular sender. This is the information I get in domino :

SMTP Server: XXXXXXXXX (XXX.XX.X.XX) connected

SMTP Server: XXXXXXXXX (XXX.XX.X.XX) disconnected. 0 message[s] received

I don’t see any more information why the sender can’t transmit the message ?

What can I do to solve this problem ? Is there a possibility to put the server in a debug mode , so I can see a lot more information in the console ?

Thanks in advance,

Karl Verhulst