Email chyba: Service unavailable - Client host IP blocked using Spamhaus

Co znamená, když se vrátí email s chybovým hlášením Service unavailable - Client host IP blocked using Spamhaus?

Celé chybové hlášení

-----Original Message-----
From: Mail Delivery System [mailto:MAILER-DAEMON@email.cz]
Sent: Monday, March 24, 2016 10:18 AM
To: test1@test.cz
Subject: Undelivered Mail Returned to Sender

This is the mail system at host smtp.email.cz.

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

email@email.cz: host misfit.example.com [8.8.8.8] said: 550 5.7.1 Service unavailable; Client host [4.4.4.4] blocked using Spamhaus; To request removal from this list see http://www.spamhaus.org/lookup.lasso (in reply to RCPT TO command)

Řešení:
Chybové hlášení nám sděluje, že odeslaná zpráva je nedoručitelná, protože odesílací SMTP server je zalistován v blacklistu (Spamhaus). Řešením je obrátit se na správce SMTP serveru ať zajistí vyjmutí z blacklistu.