The Send Review Request module will send an email to the customer, who bought an item, asking for a review. You can set how many product links will be sent, and if it's in one or two columns. You can set the order state, and the customer groups, that you wish to send the email to. You can also set the date for how old the order must be (i.e. 3 days old), and a date for how old the orders are (i.e. 30 days old). You can set if the customer needs to be a newsletter subscriber to recieve emails from this module. You set this all up, and then run a cron job. This module works with both the default productcomments, or Datakick's revws module.