I'm representing a small business with a large number of customers using @yahoo.com or Yahoo!-managed (AT&T, PacBell, etc) email services. Over the past few months, we've seen an increasing number emails sent to those domains get rejected. It's getting to the point where almost no email gets through, despite the domain we send from, which includes @gmail.com and @outlook.com.

> 554 Message not allowed - [PH01] Email not accepted for policy reasons. Please visit https://senders.yahooinc.com/error-codes

Is anyone else seeing this? Are there any known remedies?