[.] stunnel 5.46 on x86-pc-msvc-1500 platform
[.] Compiled/running with OpenSSL 1.0.2o-fips 27 Mar 2018
[.] Threading:WIN32 Sockets:SELECT,IPv6 TLS:ENGINE,FIPS,OCSP,PSK,SNI
[ ] errno: (*_errno())
[ ] Running on Windows 6.2
[.] Reading configuration from file stunnel.conf
[.] UTF-8 byte order mark detected
[.] FIPS mode disabled
[ ] Compression disabled
[ ] No PRNG seeding was required
[ ] Initializing service [smtps]
[ ] GUI message loop initialized
[ ] Ciphers: HIGH:!aNULL:!SSLv2:!DH:!kDHEPSK
[ ] TLS options: 0x03000004 (+0x00000000, -0x00000000)
[ ] Loading certificate from file: stunnel.pem
[ ] Certificate loaded from file: stunnel.pem
[ ] Loading private key from file: stunnel.pem
[ ] Private key loaded from file: stunnel.pem
[ ] Private key check succeeded
[:] Service [smtps] needs authentication to prevent MITM attacks
[.] Configuration successful
[ ] Binding service [smtps]
[ ] Listening file descriptor created (FD=676)
[ ] Setting accept socket options (FD=676)
[ ] Option SO_EXCLUSIVEADDRUSE set on accept socket
>>> [!] bind: Address already in use (WSAEADDRINUSE) (10048) <<<<
[!] Could not bind any accepting port
[ ] Deallocating section defaults
[ ] Unbinding service [smtps]
[ ] Service [smtps] closed
[ ] Deallocating section [smtps]
To temporary resolv the problem I have to change the listen port to another number. Reread the config file and let the stunnel GUI open. Then all is working until I close the GUI (not each time but most of).