As of SAP Web Application Server 6.10, SMTP (Simple Mail Transfer Protocol) is supported directly by the SAP kernel. This means that it is possible to exchange e-mails between the SAP system and any SMTP-compatible mail server without using additional external components (such as connectors or gateways). You can use any product that meets the SMTP standard as a mail server.

As of SAP Web Application Server 6.20, it is also possible to exchange faxes and text messages (pager/SMS) using SMTP. Faxes and text messages are packed into e-mails for this purpose.

Further explanation can be showed here.