Outlook add-ins are integrations built by third parties into Outlook using the new web technologies based platform. Outlook add-ins have three key aspects:
The same add-in and business logic works across desktop Outlook for Windows and Mac, web (Office 365 and Outlook.com), and mobile.
Outlook add-ins can be acquired from the Office store or side-loaded by end-users or administrators.
The Outlook items that support mail add-ins include email messages, meeting requests, responses and cancellations, and appointments. Each mail add-in defines the context in which it is available, including the types of items and if the user is reading or composing an item.
Extension points are the ways that add-ins integrate with Outlook. The following are the ways this can be done:
Add-ins can declare buttons that appear in command surfaces across messages and appointments. For more information, see Add-in commands for Outlook.
An add-in with command buttons on the ribbon
Add-ins can link off regular expression matches or detected entities in messages and appointments. For more information, see Contextual Outlook add-ins.
A contextual add-in for a highlighted entity (an address)
Mailbox items available to add-ins
Outlook add-ins are available on messages or appointments while composing or reading, but not other item types. Outlook does not activate add-ins if the current message item, in a compose or read form, is one of the following:
Protected by Information Rights Management (IRM), in S/MIME format or encrypted in other ways for protection. A digitally signed message is an example since digital signing relies on one of these mechanisms.
In the Junk Email folder.
A delivery report or notification that has the message class IPM.Report.*, including delivery and Non-Delivery Report (NDR) reports, and read, non-read, and delay notifications.
A .msg file which is an attachment to another message.
A .msg file opened from the file system.
In general, Outlook can activate add-ins in read forms for items in the Sent Items folder, with the exception of add-ins that activate based on string matches of well-known entities. For more information about the reasons behind this, see "Support for well-known entities" in Match strings in an Outlook item as well-known entities.
Outlook add-ins are supported in Outlook 2013 and later versions, Outlook 2016 for Mac, Outlook Web App for Exchange 2013 on-premises, Outlook Web App in Office 365 and Outlook.com. Not all of the newest features are supported in all clients at the same time. Please refer to individual topics and API references, to see which hosts they are/are not supported in.
Get started building Outlook add-ins
To get started building Outlook add-ins, see Get Started with Outlook add-ins for Office 365.