I believe that Fastmail went too far in simplifying their mail listing format. They need to either add more themes or (even better) allow the color scheme and which contents are displayed to be separately controlled. They decided that they needed to remove system supported user css/js due to security concerns -- I think someone got a prize for showing them the security holes.
One partial solution is to use your favorite theme and sort order but use a search to only show messages with attachments or large messages. For example, try these searches:
- HASATT - only shows messages which contain attachments (must be capitalized)
- larger:200k - only shows messages with a size > 200K
You can save searches with a simple name so you quickly use them without looking up the syntax.
Bill