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Choose a good subject line, THINK about it.
Write your mail in English language.
Send your mail in plain text format, not HTML or Rich Text because plain text will be readable for all subscribers.
Quote portions of what you are responding to, not the whole mail and remove empty quoted lines or signatures to make your message as short as possible.
Do not make test posts to the list. Ask a real question or give a real answer.
Binary (GIF, JPEG, executables) posts are not allowed. Post a URL instead or mail your binaries directly to those people who want them.