In order to make sure your recipients receive your mailing, we automatically resend any emails that have not been opened after 2 days.
If you don't want your mailings re-sent to unopened recipients, you can update this setting from your Account Settings. After you login to your account from our desktop site, hover over your name/email in the upper right corner of the page and select Account Settings from the dropdown menu. Scroll down to the Email Notifications section. You can uncheck the box next to Delivery optimizer and click Update:
If you need any help updating your re-delivery settings, please contact us.