If you get the error, “Sending email is not enabled”, its because you haven't configured this yet.
You can configure email settings using following command.
TFSConfig ConfigureMail
/FromEmailAddress:NoReplyTeamSystem@domain.com
/SmtpHost:DomainMailServer
Or just do it via the TFS Administrator Tool which you can also Enable Email Alerts.

fc2c1fb4-2f73-48d2-8c65-e643924c3f1b|3|1.7
Visual Studio, Team Foundation Server