We removed the ability to use Basic authentication in Exchange Online for Exchange ActiveSync (EAS), POP, IMAP, Remote PowerShell, Exchange Web Services (EWS), Offline Address Book (OAB), Autodiscover, Outlook for Windows, and Outlook for Mac.
This decision requires customers to move from apps that use basic authentication to apps that use Modern authentication. Modern authentication (OAuth 2.0 token-based authorization) has many benefits and improvements that help mitigate the issues in basic authentication. For example, OAuth access tokens have a limited usable lifetime, and are specific to the applications and resources for which they are issued, so they cannot be reused. Enabling and enforcing multifactor authentication (MFA) is also simple with Modern authentication.
and I will block this if it is not essential for Mailspring.
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