The below error is reporting each time when one user from my sister concern (senderdomain.com) company tries to send email to my domain receiving the following error.
This message was rejected by the recipient e-mail system. Please check the recipient's e-mail address and try re sending this message, or contact the recipient directly.
Diagnostic information for administrators:
Generating server: mydomain.com
#< #5.1.0 smtp;554 5.1.0 Sender denied> #SMTP#
Original message headers:
Received-SPF: None (edgeserver.mydomain.com:
email@example.com does not designate permitted sender hosts)
Sender domain is white listed in our spam filter, and other users are receiving emails from that domain without any issue. Can you please advise what should I need to investigate to resolve the issue.