Email blocked by AOL ??

[#1]

Sent an email and got this message back...
Subject: Mail delivery failed: returning message to sender
Date: Tue, 15 Apr 2014 19:17:17 +0100

A message that you sent to the following recipient could not be delivered due to a permanent error. ** The remote server 64.12.88.132 responded with: ** xxxxxxxx@aol.com 554: Connecting IP: 212.159.14.20 This message was created automatically by mail delivery software on the server avasout08.

Does this mean that AOL are spam blocking Plusnet mail servers?

[#2]

It could mean that x6x's mailbox is full. Or perhaps x6x has a 'me first' policy which rejects messages unless x6x has sent one to you first (I'm not sure if users still have this option).