Microsoft recently updated the iOS version of its email clientOutlook with the ability for users to enable Touch ID when accessing the app. Outlook is the first of the major email apps on iOS -- including Gmail and Apple's own stock Mail app -- to support the fingerprint security features of Touch ID.
To set up Touch ID in Outlook, navigate to the "Settings" tab within the app, and then toggle on "Require Touch ID." In addition to basic email features, Outlook provides a calendar feature and the ability to send and view documents via sharing apps like OneDrive and Dropbox, without having to actually leave the app. All of these features can now be guarded by Touch ID as well.
For anyone looking to switch to Outlook to try out the Touch ID enhancement, the Microsoft app does support other email services including Yahoo! Mail, iCloud, and Gmail.