Several of our products generate email. When they do so, they pass the email to IBM i's SMTP stack for delivery using IBM's® QtmmSendMail() API. Some of our customers use service providers to handle delivery (aka. forwarding or relaying) of email. Increasingly, email service providers are requiring encrypted communications using SSL/TLS and SMTP Authentication (i.e. Google*). At V6R1M0, IBM i's SMTP stack added support for SSL/TLS encrypted communication and SMTP Authentication.
* Most customers we talk to balk at using the free version of GMAIL when they discover that all emails will appear to come from a single email address and consequently all replies will go to a single user.
IBM® has documents that provide detailed instructions for configuring this setup:
Additional information on certificates needed by IBM i to authenticate the service provider's server can be found at SMTP STARTTLS CA Certs.