The feature can be turned on by adding the following line to `hydra.conf`
``` conf
email_notification = 1
```
By default, Hydra only sends email notifications if a previously successful
build starts to fail. In order to force Hydra to send an email for each build
(including e.g. successful or cancelled ones), the environment variable
`HYDRA_FORCE_SEND_MAIL` can be declared:
``` nix
services.hydra-dev.extraEnv.HYDRA_FORCE_SEND_MAIL = "1";
```

SASL Authentication for the email address that's used to send notifications
can be configured like this:
``` conf
EMAIL_SENDER_TRANSPORT_sasl_username=hydra@example.org
EMAIL_SENDER_TRANSPORT_sasl_password=verysecret
EMAIL_SENDER_TRANSPORT_port=587
EMAIL_SENDER_TRANSPORT_ssl=starttls
```
Further information about these environment variables can be found at the
[MetaCPAN documentation of `Email::Sender::Manual::QuickStart`](https://metacpan.org/pod/Email::Sender::Manual::QuickStart#specifying-transport-in-the-environment).
It's recommended to not put this in `services.hydra-dev.extraEnv` as this would
leak the secrets into the Nix store. Instead, it should be written into an
environment file and configured like this:
``` nix
{ systemd.services.hydra-notify = {
    serviceConfig.EnvironmentFile = "/etc/secrets/hydra-mail-cfg";
  };
}
```

                AuthenSASL