The Outbox is where you can see all your scheduled sequences, emails, reminders and calendar events in one convenient place. From your Outbox you can quickly search, edit, and reschedule any outgoing message or reminder.
To get to your Outbox hover over the Mixmax "M" in the top right corner of Gmail and click Outbox:
You can reschedule an email or multiple emails at once that are in your Outbox. Check the boxes on the left for the emails you want to reschedule, and then hover over Reschedule to change times for those items. You can even stop scheduled items using that same process.
The panel on the left allows you to filter the Outbox by the type of event.
If you're on a team in Mixmax, the Team Outbox allows you to see all the messages, sequences, and tasks that you and your teammates have scheduled. You can switch between teams using the tabs at the top of the Outbox.