New Outlook API Makes Email Signature Management Easier

API in Preview Revealed at Ignite 2020 Conference

The advent of support for roaming signatures for Outlook desktop caused some to question if the case to use third-party email signature management products had weakened. As it turned out, Microsoft delayed the deployment and the latest information published in Office 365 notification MC215017 on September 22 says:

  • We will begin rolling this out to Microsoft 365 Monthly Channel, Targeted, in late September (previously July). (This is Insiders Slow Channel which will soon be called Microsoft Beta.)
  • We expect to roll this out to the Monthly Channel, Production, in late October (previously August).

Not Easy to Manage Outlook Signatures

My experience of using PowerShell to create and update signatures for Outlook desktop convinced me of the complexity of the task. By comparison, the signatures used by OWA are much easier to manipulate. Messages generated by Outlook mobile and other email clients connected to Exchange Online are typically handled by routing the email through an Azure-based cloud service and then back to Exchange Online for onward delivery. In a nutshell, managing corporate email signatures is not easy, especially when multiple client types are involved.

A New Signature API for ISVs

Still, ISVs need to improve their software to convince potential customers that it’s best to use their products instead of relying on what Microsoft delivers. What might surprise some is that Microsoft helps ISVs, as evident in the Build Outlook Add-ins that integrate your solution seamlessly into your users’ Outlook experience session​ (yes, that’s a mouthful) from Ignite 2020.

The session features Szymon Szczesniak, the genial CEO of Code Two software (Figure 1), discussing his company’s experience of using a new Signature API to create web add-ins which work for Outlook desktop (Windows and Mac) and OWA (now), and Outlook mobile (in the future).

Code Two's CEO explains the new Signature API
Figure 1: Code Two’s CEO explains the new Signature API

As you might expect, Code Two created a web add-in to add a corporate signature to a message before it is sent. This has been possible in the past, but only by creating something like a COM add-in that had to be installed on individual workstations or distributed to sets of workstations using Group Policy Objects. The COM add-in worked by updating Outlook settings with the signature, which Outlook then applied to new messages.

What’s Possible with Signature Web Add-ins

The Signature API and web add-ins are a dramatic step forward. Signatures inserted by add-ins based on the API can be dynamic, meaning that they can be intelligent enough to detect the type of message to insert an appropriate signature. For instance, a new message might get the full treatment with a corporate slogan inserted along with user details while a reply or forward might have a cutdown signature inserted or none. If the company publishes multiple types of signature available (for instance, signatures with different graphic layouts), users can select which they’d like to use.

Finally, because the processing is done on the client before email is sent, protection applied by sensitivity labels or Office 365 message encryption works properly and solve the issues highlighted in this article, at least for Outlook clients. Challenges remain for dealing with mail traffic generated by Outlook mobile (until it supports the web add-ins) and non-Microsoft email clients, which will still need to be processed en route.

Expect December Developments

Although Code Two Software get the kudos for publicizing the new Signature API, they won’t be the only ISV to exploit the API (LetsSignIt announced that they have also been working with Microsoft to develop an add-in). I expect a batch of new products and offerings to appear soon after Microsoft makes the API generally available, expected before the end of this year. Overall, the new API will make email signature management easier to deploy and manage, and that can’t be a bad thing.


We don’t cover much about ISV software in the Office 365 for IT Pros eBook. In this case, email signature management has been such a pain for so many organizations for so long that we’re delighted to see progress in the space.

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