Google recently added a new security feature that allows users to disable access from what they call "less secure apps" - or apps that use username and password login, which is the case with most email clients, as opposed to OAuth 2.0. This does not mean Mailbird is less secure - it just means we don't support OAuth 2.0 - yet.
We may consider OAuth 2.0 support in the future, but until then the solution is to enable "less secure apps" to access your email:
For more information, please see:
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