Problem:
ActivMail 1.3.0 build 200 to 1.3.0.209 do not set the Message ID in the SMTP message header.
Consequences:
Some mail hosts may reject the mail based on this premise. AOL is the only host known to reject these messages.
Solution:
Go to http://www.cfdev.com/downloads/ and download a new copy of ActivMail (version 1.3.0 build 210 fixes this problem)