Some information about the support for OAuth 2.0 in Squirrel
Several Internet mail providers are rolling out support for OAuth2 user authentication. Starting with version 1.6.0, Squirrel supports user authentication with OAuth 2.0. Before using OAuth 2.0, you will need to setup the OAuth 2.0 authentication with your Internet hosting provider to obtain an OAuth 2.0 access token.
As Squirrel for Domino runs in the background on the HCL Domino server, it can only use OAuth 2.0 authentication methods which do not need any user interactions. These OAuth 2.0 access methods are called machine-to-machine (M2M) communications.
Google wrote in an article, that they will be limiting access to G Suite thru OAuth 2.0 in the future. Since they do not yet support machine-to-machine authentication (thru password or client_credentials grant type), we are unable to support Gmail access thru OAuth 2.0.
Other Email Providers
Basically, any email provider should be able to be used as long as it supports the OAuth 2.0 Client Credential flow.
If you know any other OAuth 2.0 provider which support a machine-to-machine authentication (without prompting the user) please let us know. We will be glad to implement them in Squirrel for Domino.