Windows Mail APP Bug - cannot turnoff "digitally signed" option when replying a signed email.

Hi everyone,

I have encountered a problem that, if someone send me a digitally signed email to my outlook account, and if I try to reply this email, then Windows Mail App will automatically turn on the "digitally signed" option, causing me not able to send the reply because "signing certificate is missing, invalid, or expired."

I learned that it is possible to configure the digital signing in Windows Mail App (https://learn.microsoft.com/en-us/windows/security/operating-system-security/data-protection/configure-s-mime#digital-signatures). However this option seems only available for Exchange account, and for outlook account, there is no such option.

See screen shot here:

there is a symbol on the right side of the subject box, saying that the reply message will be "digitally signed". This symbol seems inherited from the incoming digitally-signed email and cannot be turned off (replying a non-digitally-signed email does not have this issue).

The reply cannot be sent and this error message shows up

This issue is very annoying because there is no way to reply this message. and if you know a solution to this issue, it would be super helpful.

Thanks a lot!