Ok before I begin I would like to say how much html emails suck. I have learned some rules with html emails that I would like to share. Share your email tricks of the trade as well!
1. Table Driven - this is a given.
2. Can only apply padding directly to the td itself.
3. Any element inside the td margins must be applied to.
4. Setting a border for the parent table is quirky across email clients.
5. If I set a fixed width to the parent table itself I set %'s for the children TDs. e.g.
<table summary="...." cellspacing="0" width="730">
With emails you have to suck it up and basically step backwards in technology.