Failed to Connect to SMTP host

I am running Lotus Domino from a file server in WINNT based LAN. Within LAN there is a proxy server running on a different Machine which i am connected to a Local ISP.
From the Lotus Domino server Machine i can browse i and receive mails includingLotus mails But unable to send out.
The error it displays is:
Router: Failed to Connect to SMTP host SMTPOUT.SWIFTKENYA.COM because server not responding.

Where swiftkenya.com is my ISP.
I have confirm with that there server is working well.What might have happened in my domino server?. Please assist. Thanks