AOL mail domains have started to embrace DMARC more explicitly, much like their Email brethren, Yahoo. You may have started seeing bounce messages with the reason of:
"521 5.2.1 : (DMARC) This message failed DMARC Evaluation and is being refused due to provided DMARC Policy"
This is because AOL will no longer be accepting messages where the From domain is an AOL mail domain, and the message originates from a non-approved AOL mail domain server/service. This is a security measure they have implemented to help reduce potential address spoofing of their mail domains.
What this means: You can no longer send with the From address being anything from an AOL address when sending to a domain that checks DMARC before accepting mail.
What you can do: You will need to change the From address to a non-AOL address. We recommend using your own mail domain, or one you control that is legitimate. You can then set the Reply-To field to be the original AOL address that previously was used in the From field.
What about these messages, are they lost ? Yes, any send with this bounce message is discarded and tracked as a Block. You will need to adjust your From address field settings, and then try resending from your side.