Markdown horizontal line being generated with only two '-'

The Markdown syntax for a horizontal line is "by placing three or more hyphens, asterisks, or underscores on a line by themselves", however, MailMate generates a horizontal line with only two. This is a problem because the "standard" signature break detector for email is "--[space][enter]".

I use this in my signature as it helps our Service Desk system detect the beginning of the signature in email responses, and I suppose other systems use it as well, for which it won't break as they read the plain text version, but when I'm sending mail to other people, I think it looks wierd to have a horizontal line on the signature...