Windows 2016 Server: [!] bind: Address already in use (WSAEADDRINUSE) (10048)

Hello List

My problem:
If I run stunnel I regular get the below error:

[.] 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) <<<<
[!] Error binding service [smtps] to 192.168.10.62:11465
[!] Could not bind any accepting port
[ ] Deallocating section defaults
[ ] Unbinding service [smtps]
[ ] Service [smtps] closed
[ ] Deallocating section [smtps]

I had the same problem with the previous versions aswell.

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).

My system:
- Windows 2016 Server
- stunnel-5.46
- stunnel installed as service and GUI

My config file (relevant part):
taskbar = yes
client=yes
[smtps]
;delay = yes
accept = 192.168.10.62:11466
connect = server.domain.ch:465
cert = stunnel.pem
local = 192.168.10.53 (this is dedicated address)

I found a similar threat in the  archives (but on Linux):
https://www.stunnel.org/pipermail/stunnel-users/2018-February/005935.html

Here is Microsoft's describtion about WSAEADDRINUSE) (10048):
https://msdn.microsoft.com/en-us/library/windows/desktop/ms740668(v=vs.85).aspx

All helps are welcome.

Kind regards,

-- 
Martin Schweizer

PC-Service M. Schweizer GmbH; Bannholzstrasse 6; Postfach 132;
CH-8608 Bubikon; Tel. +41 55 243 30 00; Fax: +41 55 243 33 22

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