I'm trying to email somebody who chose my answer as best answer.?

Not all users allow email communication

I'm sure you are aware you can check to see if the user allows email by clicking their profile and seeing if they allow a user to email them by clicking the send .... an email.

Not all users will have this option enabled.

If this is the case I would leave a comment on the closed question and hope they read it. This can be done via the comments box

All the best

Chεεrs

you can only email them if they allow it. Alternatively, you can add a comment to your answer <via edit> to ask them to email you, you can always add them to your contacts and then when they are notified they may opt to communicate with you

learn how to spell first....