Editing Stunnel (section)

==Example==
A stunnel can be used to provide a secure [[Transport Layer Security|SSL]] connection to an existing non-SSL-aware [[Simple Mail Transfer Protocol|SMTP]] mail server. Assuming the SMTP server expects TCP connections on [[Port (computer networking)|port]] 25, the stunnel would be configured to map the SSL port 465 to non-SSL port 25. A mail client connects via SSL to port 465. Network traffic from the client initially passes over SSL to the stunnel application, which transparently encrypts and decrypts traffic and forwards unsecured traffic to port 25 locally. The mail server sees a non-SSL mail client.{{citation needed|date=October 2019}}

The stunnel process could be running on the same or a different server from the unsecured mail application; however, both machines would typically be behind a firewall on a secure [[internal network]] (so that an intruder could not make its own unsecured connection directly to port 25).{{Citation needed|date=October 2023}}