On Wed, 2010-03-24 at 08:27 -0430, Patrick O'Callaghan wrote:
possibly somewhere along the line the HTML is being reflowed or in some way modified, which would destroy the signature. I can't really see how that could happen
We've seen plenty of plain text message parts being transcoded in transit by some allegedly "helpful" mail server (turning quoted printable into 8-bit, etc.). I wouldn't be the slightest bit surprised at a mail server doing the same sort of thing to text/html content.