what does this error mean?

[shawshank62]

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

XXXXXX@hotmail.com
SMTP error from remote mailer after RCPT TO:XXXXXX@hotmail.com>:
host mx3.hotmail.com [65.54.167.5]: 550 Requested action not taken:
mailbox unavailable

This person was signing up for a membership to my forums, and i recieved that email. I was curious as to whether the error is on my side, or hotmail?

[Shifter2101]

SMTP error "from remote mailer after RCPT" (RCPT=receipt)

aka ... after you sent the message to this person.

..."permanent error" AND "mailbox unavailable".

error not on your end. your most likely sending mail to a bogus email address. either they handed you a fake one or they/you misspelled it. (my $$$ is on "they").

hotmail accts go inactive after about 30 days FYI.

edit** when i say they misspelled... i mean while they were filling out the signup form @ your forum.

[shawshank62]

thanks shifter