I tried with many different files so you can try any you want but I sent to you the link to one of because I didn't found the ability to add file in PM.can you pm me with the file you try to attach so i can try it on my end ?
Take any proper email client, like thunderbird or outlook express (yes, it works under windows after xp via runasxp) or outlook or pegasus or eudora or etc, and they will allow the creation of plain text messages with attachments. I hear what you say, but from a user point of view, it looks like it needs to be there, so if you really want to avoid it, then perhaps inform about it nearby the plain text option or so? But better have it, as it will always create trouble when missing.A truly plain-text message can't have attachments because it's nothing but text, adding attachments makes it a multipart message, which simply beats the purpose of such emails.