As the lead developer of the application that creates the emails @artur talks about: Yes, we could change it (or use ^^^^ instead of ---- in the “underline”), but this is technically not markdown but simply a text/plain email that’s formatted in a “nice” way for humans. And the “underlined” headings do look a bit nicer IMHO than using markdown-style # something headings
Anyway, don’t email signatures that are delimited with -- usually have a blank line right before the -- line? So maybe that could be taken into account when parsing emails?