saop adds authentication to any SMTP server by using a POP3 or IMAP4 server as the authentication backend. To do so, it sits in the middle of an SMTP session and intercepts login attempts. It then captures the user and password and authenticates against a POP3 server, an IMAP4 server, or a password list.
sendPGPMail.cgi is a small CGI script for sending an encrypted PGP email message to a predefined receiver from an HTTPS secured Web page. The typical use of this script is to provide the users of a secure Web site the possibility to send a secure email to a predefined employee of a company. The CGI script gets its input from an HTML form and passes it on to gpg. The message and its attachments are encrypted using the PGP public key of the predefined receiver.
sendmail X is a modularized message transfer system consisting of five (or more) persistent processes, four of which are multi-threaded. A central queue manager controls SMTP servers and SMTP clients to receive and send email messages, an address resolver provides lookups in various maps (including DNS) for mail routing, and a main control program starts the others processes and watches over their execution. The queue manager organizes the flow of messages through the system and provides measures to avoid overloading the local or remote systems by implementing a central control instance. sendmail X is simple to configure using a syntax that is easy to understand and use. It is intended to be used as a secure and efficient mail gateway. It does not provide any mail content modification capabilities such as address masquerading.
Sendmail-TLS is a wrapper for Sendmail which allows for clients to make a secure (SSL) connection to their mailserver as described in RFC 2487. The connection is internally forwarded to sendmail and does not require sendmail to be running on port 25. Clients which support this currently are Netscape Messenger, Microsoft Outlook, and Microsoft Outlook Express.
sendqmailq is intended for home computers that run qmail as their MTA but do not have permanent connection to the Internet. The outbound emails are stored locally in a queue, and when the IP connection is brought up, sendqmailq sends them to the ISP's SMTP server. Unlike serialmail, sendqmailq sends one single copy of an email to multiple recipients (instead of one copy each).