521 Recipient address rejected
This error indicates that the AOL member email address no longer exists or the address is misspelled.
AOL will not accept delivery of this message
This is a permanent bounce due to:
RFC2822 From domain does not match the rDNS of sending server.
RFC 2822 FROM address does not have an A record and is not a valid domain.
IP has a poor reputation and mail is sent to multiple recipients.
There are multiple From address in the mail headers and the IP reputation is poor.