For inbound emails this is worth very little as if avast alerts you will know all about it as all hell breaks loose with an audible and visual alert.
For outbound email yes it is a little promotion for avast

You don't say what your email client is ?
So the above suggestion by nmd is for MS Outlook and not Outlook Express.
So if you aren't using MS Outlook, then it is the Internet Mail provider, Customize, SMTP, enable 'Insert note into clean message.'