The stunnel program is designed to work as an SSL encryption wrapper between remote client and local (inetd-startable) or remote server. It can be used to add SSL functionality to commonly used inetd daemons like POP2, POP3, and IMAP servers without any changes in the programs' code. Stunnel uses the  library for cryptography, so it supports whatever cryptographic algorithms are compiled into the library. 

Stunnel can benefit from  validation of the OpenSSL FIPS Object Module, as long as the building process meets its . A scanned  document is available for download on the . The  is compiled with FIPS 140-2 support. The FIPS mode of operation is no longer enabled by default since stunnel 5.00. 

Stunnel is a free software authored by . Although distributed under , stunnel is not a community project. We retain the copyright of the source code. Please  for commercial support or non-GPL licenses. Free, community-based support is also available via  mailing list. 

The obsolete 3.x branch is no longer maintained. Use  perl script as a drop-in replacement for backward compatibility.

 

reference from：https://www.stunnel.org/index.html