Emails returned by hotmail

Question

Some emails I send (from php) are returned by hotmail with this message:

<xxxxxxx@hotmail.com>:
User and password not set, continuing without authentication.
65.55.92.136 does not like recipient.
Remote host said: 550 Requested action not taken: mailbox unavailable
Giving up on 65.55.92.136.

I understand that the recipient has no mailbox. But what does that mean:

"User and password not set, continuing without authentication."

And what can I do to avoid it?

I use linux/qmail.

EDIT : I am not using hotmail to send emails. I am sending emails to some hotmail users.

Answer 1

The e-mails doenst exist.

Answer 2

You qmail servers SMTP route specification file does not contain a username/password line for mx1.hotmail.com/mx2.hotmail.com. You probably misconfigured SMTP AUTH with your relay host.