As a guest, if your host has opted to leave the invitation's activity feed public, you will receive periodic emails when other guests have made activity on the feed. The activity feed is a private social feed that allows hosts and guests to interact with each other. Some of the activity feed interactions that can trigger these emails are: guest comments, photo uploads, interaction with the host-created various widgets, etc. If you would like to stop these emails, you can simply access the invitation and click the "Settings" tab and use the checkboxes to disable the email notifications.
These emails are different than our marketing/promotional emails, and are only being sent to you as a result of your interaction with the invitation. If you wish to stop these specific emails, you will need to do so using the instructions above.