Never mind. Problem was due to my pasting in a table from Open Office calc spreadsheet. A native table works as expected, and once I pasted my table into Komposer I could play with the source. The HTML Open Office pastes is not quite as bad as anything from Excel or Word, but it did have the style rule

frame="void" rules="none"

as part of the table tag. Once I erased those, I went back into "Normal" view, then I pasted the table back into T-bird. Nice enough, the presence of those rules in Komposor also suppressed the border, so it was obvious I fixed things once I erased that part of the table tag in the "source" view.

It would be nice to have a function in Blue Griffon or Komposer that just strips every single thing out of a table so it is at its 'rest state'.

New suggetion, paste spreadsheet tables into Blue Griffon (or Komposer if you want to span cells) and mess with it there, get it looking the way you want with inline styles, and then paste that into Thunderbird.

Live and learn.

OK, next problem was getting the table borders collapsed. The rule border-collapse: collapse; is a CSS rule and you can't bury inside a table tag. I know, I tried. So it turns out the 'rules' advanced attribute is really your friend. Change it from "none" to "all" and the double-line borders to all collapse. Yippee.

So now I see you don't really need to go to Komposer or BlueGriffon to get a table pasted from Open Office Calc to look presentable. Click a cell in the table. Click the little blue screen drop down (WTF?) to the left of the smiley face in the toolbar. Select "table". When that dialog box comes up, change the top tab from "Cells" to "Table". Click the "Advanced Edit" button on the lower right. Click on the "rules" attribute (or create it) and use the bottom right drop-down to select "all". Hit OK. Now back in the Table Properties dialog box, you can hit "Apply" button on the bottom and you should see the change. Keep suffering, its builds character.

Of course, all these attributes no longer work in HTML 5, so who knows what joy awaits us huddling masses in the future?

Until Microsoft crawls out of the 20th century with regard to HTML 5 in email I think nothing much will change. AFAIK Outlook and the rest of their email stable still so not fully support CSS and until they do they have no hope of fixing the font and other text attributed they attach to about every second word. Likewise Gmail support is also pretty lame. There will have to be lots more green onthis page before HTML5 mail can become mainstream.