Any option I try in stunnel 5.55 results the same. Say: 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