Email will relay if sender is empty ???

[fremann]

Hi there.
I have a WinNT 4.0 and Exchange 5.5 SP4 with the SP4 bug fix installed.
Recently a lots of emails queue in my Internet Mail Connection. Then I try to telnet to the smtp and this is what I found.

mail from:me@domain.com
250 OK - mail from <me@domain.com>
rcpt to:you@otherdomain.com
550 Relaying is prohibited

This is what I want. But if I go another way, here what is happened.

mail from:me@domain.com
250 OK - mail from <me@domain.com>
rcpt totherdomain.com
250 OK - Recipient <otherdomain.com>

Why this happens? Can anyone help me?

Regards,
Victor