As a user, there may be times that you want to target people who opened a message with more communication. Or you may want to export a list of people who received a message.
Using the Statistics Tagging feature you can do both of these.
Open the email you are interested in and click on the Statistics button.
Click on the statistic you want to tag
Click on the "Tag These Accounts" button
The system will now tag all of the accounts one at a time in the background. From here, you can switch to the Accounts tab and create a segment that targets these Accounts. From there you can export the segment or use the segment to create a campaign or blast.