Please forgive my flare for the obvious if you already are aware of the following.
There are so many possiblities of why this might happen. Max may be mass mailing off of the same IP block and thus get put into the bulk filter. The IP's for Epic may be new, it may also be the way the text and images interact on the html page. The number of images, the domain the images are linked to may have flagged words. The % of html vs text in the message. The color of the text, whether there is Rot13 in the message, has ReverseDNS been setup correctly, words in the subject line, wording like "unsubscribe", any variables being passed such like
http://www.whatever.com/?variable=test etc. etc. etc.
These things are all scored and tallied for a final count that determines whether or not you end up in the bulk filter. It was interesting working against the Baysian Filters Hotmail put in place. It is like working against a boa constrictor if your sending in legit mail from a legit closed looped system.
Do an nslookup and throw the ip's into spamhaus and some other DNS blacklist sites.
Hope this helps. If you really need to know, send me the two messages and I may be able to tell from the way the creatives were done. If its not the creatives its a network issue.
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