You can now write add-ins for Outlook on iOS

You can now write add-ins for the Outlook iOS mobile application! Ever since the add-in development model was re-launched to make use of HTML and JavaScript, it was “the dream” to have add-ins which would run on all the different places that users consumed Office applications. We’ve seen that happen with Office365 and the web-based offerings, and more recently on Office for Mac, and it’s great to now see these same add-ins available on mobile clients as well. You can read the full announcement on the Office Dev Centre.

Once added, users can launch your add-in from within the main canvas of the application:

There are a few caveats though. Although the technology stack is the same as for other platforms (HTML & JS); the reality is that the layout might be slightly different to cater for consumption on a mobile device.

It sounds Microsoft will be fairly strict about vetting which apps they enable though – it’s not going to be a free-for-all. There are initially 6 steps potential mobile add-in developers need to go through, starting with a ‘pre-approval’ process:

1. Add-ins that support mobile must pass a strict set of validation criteria, so we encourage you to share your scenario ideas and mockups for pre-approval before you start implementation, using the form at https://aka.ms/outlookmobileaddin.
2. Decide what scenarios to enable on mobile. Not every action makes sense on the small screen, so be sure you’re highlighting the most important functionality of your add-in for mobile. Keep in mind that only mail read scenarios are supported right now.
3. Update your manifest to declare support for the Mobile Form Factor and define the actions you came up with in step 1.
4. If applicable, make sure any backend calls to the mailbox are using our REST API. EWS requests are not supported on mobile.
5. Build mobile-specific UI for the small screen using our design guidelines.
6. Submit your add-in to the Office Store for validation. You can find instructions here.

For more information about this process you can also visit the documentation for writing add-ins for Outlook Mobile in Office Dev Centre.