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The OAuth2 authentication process starts normally. However, after I click "Allow" in Thunderbird to grant access to my Gmail, I encounter an error stating: "Failed to establish a secure connection to localhost." The specific error code is SSL_ERROR_INTERNAL_ERROR_ALERT.

I have already tried adjusting settings related to cookies and JavaScript, but it didn't resolve the issue.

From Microsoft: "Recent Outlook Mobile updates introduced a stricter and more standards-aligned S/MIME message structure. The messages themselves are valid, but some third‑party mail clients such as Thunderbird do not fully support the way Outlook mobile structures the encryption. As a result, these clients may display a blank message body even though the encrypted content is present.

As a workaround, if you need to send encrypted mail to recipients who use third‑party clients, use Outlook desktop or Outlook on the web instead of Outlook mobile. These versions generate encrypted messages in a format that is more widely supported. "

I couldn't find this reported anywhere in these forums. Is there a solution being worked on to address this issue? Or has anyone found a workaround? We are stuck with using the Outlook app until the Thunderbird app supports S/MIME.