Microsoft now allows you to create tasks in Outlook iOS app. To follow up on an email, you can just go to options […] menu and create a task. If you go to the Microsoft To Do app, you can view your newly created task along with other tasks.
Like the other tasks which you have added in the To Do app, you can set due dates and reminders for this newly created task.
This new tasks feature is now available for Outlook Insiders with version 4.47.0 (5163338). You can expect this feature to be available for all users next month.
You can download the latest Outlook app here from App Store.