In order to enable the Mail system you have to go under Settings -> Mail and fill ALL the following fields:
Username: the username for authentication
Email Address:
Password: the password for authentication
SMTP Host: Hostname of the SMTP server
SMTP Port: Port number of the SMTP server
SMTP Secure: Security type for the connection (SSL, TSL, No secure)
Use SMTP: it is necessary to set it on TRUE. If false, the system doesn't use the SMTP server configured above.
If you use your local mail server for relay (for example POSTFIX or SENDMAIL) please see the file /var/log/maillog in order to check that everything is correct