Undelivered Mail Returned to Sender

Dobry den,

neleze nam posilat maily z nasi domeny vytvorene u vas na domeny seznam.cz a email.cz

Koncem roku 2020 vse fungovalo, maily na seznam.cz sly posilat, nyni nam to nejde a vraci se nam to s nasledujici chybou:

this is the mail system at host wes1-so1.wedos.net.

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

<@seznam.cz>: host mx1.seznam.cz[77.75.78.42] said: 550 5.7.1 Sender
Policy Framework of `kookoi.com‘ domain denied your IP address. (in reply
to MAIL FROM command)

Reporting-MTA: dns; wes1-so1.wedos.net
X-Postfix-Queue-ID: 4DW2VM095szBY1
X-Postfix-Sender: rfc822; koo***@ko****.com
Arrival-Date: Wed,  3 Feb 2021 14:25:14 +0100 (CET)

Final-Recipient: rfc822; a***.f****@seznam.cz
Original-Recipient: rfc822;a***.f****@seznam.cz
Action: failed
Status: 5.7.1
Remote-MTA: dns; mx1.seznam.cz
Diagnostic-Code: smtp; 550 5.7.1 Sender Policy Framework of `kookoi.com‘ domain
denied your IP address.

Muzete nam prosim poradit ,co s tim mame delat,nebo kde je problem? Nejsem zadny specialista, tak prosim jestli muzete jednoduse a jazykem smrtelnika. Moc Vam dekuji