PS C:\Program Files (x86)\stunnel\bin> .\stunnel \path\to\config\file

[ ] Running on Windows 6.2

[ ] No limit detected for the number of clients

[.] stunnel 5.55 on x64-pc-mingw32-gnu platform

[.] Compiled/running with OpenSSL 1.1.1c  28 May 2019

[.] Threading:WIN32 Sockets:SELECT,IPv6 TLS:ENGINE,OCSP,PSK,SNI

[ ] errno: (*_errno())

[ ] GUI message loop initialized

[ ] Running on Windows 6.2

[.] Reading configuration from file stunnel.conf

[.] UTF-8 byte order mark detected

[ ] Compression disabled

[ ] No PRNG seeding was required

[ ] Initializing service [ssh]

[ ] Ciphers: HIGH:!aNULL:!SSLv2:!DH:!kDHEPSK

[ ] TLSv1.3 ciphersuites: TLS_CHACHA20_POLY1305_SHA256:TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256

[ ] TLS options: 0x02100004 (+0x00000000, -0x00000000)

[ ] No certificate or private key specified

[:] Service [ssh] needs authentication to prevent MITM attacks

[ ] Initializing service [gmail-imap]

[!] Service [gmail-imap]: TLS server needs a certificate

[ ] Deallocating section defaults

[!] Server is down

Same with

PS C:\Program Files (x86)\stunnel\bin> .\stunnel nonexistent

or

PS C:\Program Files (x86)\stunnel\bin> .\stunnel -help

Regards, Clodoaldo