open Admin>Emails and check Send email via SMTP instead of local mail box
and if you are using your gmail for activation then set this options:
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.