swaks' primary design goal is to be a flexible, scriptable, transaction-
oriented SMTP test tool. It handles SMTP features and extensions such as
TLS, authentication, and pipelining; multiple version of the SMTP
protocol including SMTP, ESMTP, and LMTP; and multiple transport methods
including unix-domain sockets, internet-domain sockets, and pipes to
spawned processes. Options can be specified in environment variables,
configuration files, and the command line allowing maximum
configurability and ease of use for operators and scripters.

Homepage:
https://www.jetmore.org/john/code/swaks/
