Hello, sometimes i have messages from other email servers like this: This is the mail system at host szpital.slupsk.pl. 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 protected]>: host example.com[xxx.xxx.xxx.xxx] said: 550 5.7.1 Client host rejected: cannot find your hostname (in reply to RCPT TO command) I have DNS on other server than ISPConfig, I have SPF set. Where find solution?