Go in General Parameters > Advanced Parameters > SMTP:
Session key containing mail address: choose which session field contains mail address
SMTP Server:
IP or hostname of the SMTP server
SMTP Port: Port of the SMTP server
SMTP User: SMTP user if authentication is required
SMTP Password: SMTP password if authentication is required
SSL/TLS protocol and SSL/TLS options: Here you can enable SMTPS or startTLS
If no SMTP server is configured, the mail will be sent via the local sendmail program. Else, Net::SMTP module is required to use the SMTP server
The SMTP server value can hold the port, for example: mail.example.com:25
If authentication is configured, Authen::SASL and MIME::Base64 modules are required
Mail headers:
Mail sender: address seen in the "From" field (default: noreply@[DOMAIN])
Reply address: address seen in the "Reply-To" field
charset: Charset used for the body of the mail (default: utf-8)