Mail error

I receive an error message from systemadmin when i send a mail saying, message undeliverable.

The message is as follows.
Your message did not reach some or all of the intended recipients.
Subject: FW: VIPA-Modules

Sent: 12/20/2004 3:42 PM

The following recipient(s) could not be reached:

'info@vipaesa.com' on 12/20/2004 3:42 PM

503 This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.

'saravanan@vipaesa.com' on 12/20/2004 3:42 PM

503 This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.

Why is this happening? What should I do?

Are YOU running your own email server? or are you using someone elses?

Are your Rev. DNS records set up correctly. Many times this bounce error is due to the reciepiant server being unable to verify the sending server {you}.
They block those to help stop spam.
Check your DNS records at: www.dollardns.net. choose the DNS Crawler, input your IP, push submit query.
If no SOA record is returned ~ that is your first step in fixing the issue