I'm not a moderator but you need to make sure that your email client is set so the messages going to the mailing list are plain text only. Rich text and HTML formats (along with anything else that isn't good old US-ASCII) are actually coded as attachments in the email.
In general, if you see text in italics, bold, color, underline, different type sizes, or typefaces, etc, it will be sent as an "attachment".
If you can't do on a bottom of the line portable typewriter from 1967, then it will be sent an attachment. And even those often have two-color ribbons :-) Can't do that here.