How to insert custom fields in between Outlook's New Mail form?

Question

We want to create an Outlook add-in which customizes the New Mail form (Message class) of Outlook such that our custom region appears embedded, below the attachments bar of Outlook, as shown in this mock-up:

So far, the options we've explored are Form Regions and Form Page customization. Form Page customization allows us to add controls at the required place, but the theme of the form is lost. Form regions, by limitation, cannot insert custom regions in between existing form.

How can this be achieved without changing the theme of the form? Please note, the add-in would be using C++ or .NET for coding.

Answer 1

The short answer is you cannot do it without changing the theme of the form. Regardless, I would not recommend building a solution using the legacy Custom Form approach. Custom TaskPanes are out as well as they can only dock to the window borders.

The long answer is the hard answer, using the Windows API to inject your UI: https://code.msdn.microsoft.com/OlAdjacentWindows . However, this approach is not supported.

Answer 2

The way forward for Outlook integrations are the new web based add-ins See here. . Granted, they won't allow you to integrate as nicely within the form, but the default Outlook task panes do actually integrate directly below that form, and on the positive side, it allows you to go cross-platform which would be impossible in any of the legacy extensions.