Hoople - 4:54 am on Mar 1, 2013 (gmt 0)
make the content as little "spammy" in nature as you can. Write it neutral and factual, avoid all marketing flair. You've already sold them to get an account anyway.
There are online SPAM factor checking services. Try a few and see if you message can be revised slightly to achieve the same buy factor.
Some have taken extra freestanding URL's and moved them to their logo image. There are marketing sites offering more tips besides what has been said here (all very valid).
An old time email guy...