Unable to Deliver message 554 5.7.1 HELO/EHLO domain is invalid

Some domains cannot send mails to your domain and report error: 554 5.7.1 This message has been blocked because the HELO/EHLO domain is invalid.

554 5.7.1 This message has been blocked because the HELO/EHLO domain is invalid.

Go to your Email Profile in Firewall and click edit.

Remove HELO DNS Lookup option.