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Forum Moderators: phranque
Go with what Marcia suggested, plain text (unless you have an option set up if they want plain text or HTML).
Plain text doesn't have to be attached, downloads very quickly and is the "safest" way to send emails (if the email is set up as plain text then you cannot put in hidden code for viruses etc..).
My own newsletters are plain text because I started them when I had these problems and assumed that others at work may be in the same position.