Recipient address rejected

[deloptes <deloptes@gmail.com>]

Hi
I think it was already discussed here, but I may have missed the point.

What does it mean

>From yahoo I get:

This is the mail system at host localhost.localdomain.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                  The mail system

<debian-user@lists.debian.org>: host bendel.debian.org[82.195.75.100] said:
550
    5.7.1 <debian-user@lists.debian.org>: Recipient address rejected: Mail
    appeared to be SPAM or forged. Ask your Mail/DNS-Administrator to
correct
    HELO and DNS MX settings or to get removed from DNSBLs; MTA helo:
    localhost.localdomain, MTA hostname: unknown[221.224.30.132]
(helo/hostname
    mismatch) (in reply to RCPT TO command)