This is a mail with a couple of long lines and then a sig. This is used as test of the format=flowed output in the nsHTMLToTXTSinkstream. If this test fails and none else, it's likely the spaces at the ends of the lines that are missing. They aren't easily seen without looking at the data in an editor and checking where the end of line is.
Testing Space stuffing
From shouldn't start a line.
> neither should a greater then symbol.
Nor a space.
--
Above is NOT a sig delimiter since it's missing the trailing SPACE:
--
Above is a sig delimiter. I hope.
A sig (wow!).