How can this be fixed?

Good day! I cannot receive a forwarded letter from a Ukrainian company: Unknown error: permanent error (550): [email protected] is blocked because of sending spam. Contact [email protected] for additional information. For their part, they cannot solve it.

Hi,

It could be that your DNS isn’t properly set up for spam protection. Try sending a test message to the address at this site: https://www.mail-tester.com/

It should test your message for proper DNS settings.

Apart from that, you can refer to the following docs on Troubleshooting Email Issues