At Admin Panel -> Emails -> Send Emails, you can write an email and send it out to members or topic submitters who meet your specified criteria. You can use any member template variables in this message, and they will be automatically replaced with the proper value for the person who is reading the particular email. You can also use toplists.

Be sure that you've set the conditions for who will get this message using the selectors near the top of the page. If you only want to send to member who have submitted at least one topic, for example, you would choose where topics is greater than 0.

You may also send to all members or all topic submitters simply by selecting that option.