Over all this is not too bad. It at least separates the areas well and doesn't make it unreadable. It is, however, a little too busy, from a visual design perspective, which gives it a "messy" feel. There are also a few problems I noticed with the HTML:
The objective is a tighter, cleaner look for the interface. The main points were to eliminate the cumbersome white lines between all of the cells and any superfluous text or elements. The HTML was also simplified and an outer table was used to add a much better looking border than the crappy borders that browsers draw when using "BORDER=". Take a look at the HTML source. Also, the two text boxes for the Subscribe and Unsuscribe messages were moved to the bottom to be spread across the entire width so that they could be wide enough to hold the full width of the message text. They are 70 characters wide and use WRAP=HARD.
Here's the same page layout but using CSS instead of a bunch of COLOR= in the tags. This can make it easy to change the look (as in examples 2 and 3 below). The style sheets are just inside a STYLE tag in the HEAD in these examples, but you'd probably want to have them in a separate file--purhaps generated from the mailman options program-- and just link to that file in the HEAD section of the pages.
This is exactly the same, just with the CSS specs giving the page an all-blue look.
Same thing but with an all-green look. This mockup demonstrates the one kink in the style sheets solution: Netscrape doesn't seem to understand a background and color specification for the BODY tag! The above two mockups, for example, should have had a light grey background, and this mockup should have a black background with white text. Even Netscrape 4.5 completely ignores the BODY { background-color: #000000; color: #FFFFFF } style sheet.