A person may be having trouble receiving mail from a specific email address, domain, or network on their GreyMail account. The sender may be receiving a 571 error code.
GreyMail protects users inboxes by using industry standard practices, such as Sender Policy Framework (SPF) and DKIM mail authentication techniques. The most common cause of this error is due to poor email server setup.
The below example error may not look exactly like the below:
571 Delivery not authorized, message refused
Please have the sender contact their IT department or whoever manages their email server. This is not an issue on GreyMail's end.