For each target, a child process is spawned by shmux, and a shell on the target obtained one of the supported methods: rsh, ssh, or sh. The output produced by the children is received by shmux and either (optionally) output in turn to the user using an easy to read format, or written to files for later processing making it well suited for use in scripts.

For more details, check out the shmux(1) manual page. The example shown on this page is also a good illustration of some of shmux's capabilities and is dissected frame by frame for your convenience.

To take full advantage of shmux you will need to have fping installed.

Bounce Address Tag Validation (BATV) provides a mechanism for assessing the validity of an email's envelope return (bounce) address. It permits the original submitter of a message to sign the SMTP MailFrom address. This enables detection of invalid bounce addresses.

Wikipedia Excerpt

The basic idea is to send all e-mail with a return address that includes a timestamp and a cryptographic token that can not be forged. Any e-mail that is returned as a bounce without a valid signature can then be rejected. E-mail that is being bounced back should have an empty (null) return address so that bounces are never created for a bounce and therefore you can't get messages bouncing back and forth forever.