If you receive the error
554 Message not allowed - [PH01] Email not accepted for policy reasons [120] from Yahoo Mail it means that Yahoo detected a problem in the content of your email such as a virus, spam, phishing content. If you wish to appeal the problem, after confirming that there was not an issue with your email, you can
contact the Yahoo Postmaster Team with the complete information such as full email headers, the original message body, and plain text links.