Hello again from the team at Symprex.

Our teams have been working hard to prepare for Microsoft's launch of a new method for Outlook add-in authentication called nested app authentication (NAA). NAA replaces the current authentication method, which Microsoft now refers to as "legacy tokens".

The preferred solution to this change is to upgrade the add-in to version 3.0. This will ensure that you are using the latest version of the add-in, and are able to take advantage of the newest updates and features.

As part of this process you will be asked to grant admin consent to two new permissions ("Maintain access to data you have given it access to" and "Sign in and read user profile"). This does not grant Signature 365 any additional access to data but is required for NAA to work.

Updating the Signature 365 modern add-in

If you are unable to perform the upgrade at this time, please see the following article for additional options:

Nested app authentication (NAA) and deprecation of Exchange legacy tokens