[stunnel-users] Connection never completes

Mario Ricciardi spam at ocode.net
Wed May 22 06:49:14 CEST 2019

I have Stunnel on two computers, both Win10 version 5.54.  One works
flawlessly on my home network, but the second will not complete the
connection to POP3 Office365 on the work network.  It gets to s_connect and

2019.05.21 22:50:19 LOG7[main]: Found 1 ready file descriptor(s)

2019.05.21 22:50:19 LOG7[main]: FD=220 ifds=r-x ofds=---

2019.05.21 22:50:19 LOG7[main]: Service [POP3 Incoming] accepted (FD=780)

2019.05.21 22:50:19 LOG7[main]: Creating a new thread

2019.05.21 22:50:19 LOG7[main]: New thread created

2019.05.21 22:50:19 LOG7[2]: Service [POP3 Incoming] started

2019.05.21 22:50:19 LOG7[2]: Setting local socket options (FD=780)

2019.05.21 22:50:19 LOG7[2]: Option TCP_NODELAY set on local socket

2019.05.21 22:50:19 LOG5[2]: Service [POP3 Incoming] accepted connection

2019.05.21 22:50:19 LOG6[2]: failover: priority, starting at entry #0

2019.05.21 22:50:19 LOG6[2]: s_connect: connecting

2019.05.21 22:50:19 LOG7[2]: s_connect: s_poll_wait
waiting 10 seconds


The sessions stay active, but this is as far as they get.  I start stunnel
GUI and attempt to connect to the active port and the above behavior is what
I get.  


Using OpenSSL I can connect just fine, so there doesn't appear to be a
firewall issue:


+OK The Microsoft Exchange POP3 service is ready.


user LoadAccept at example.com


pass LAxxxxxx

+OK User successfully logged on.


+OK 4 356828

1 70284

2 70415

3 108104

4 108025


The stunnel config is super simple:



; Debugging stuff (may be useful for troubleshooting)

debug = 7

output = stunnel.log

; **************************************************************************

; * Service definitions (at least one service has to be defined)           *

; **************************************************************************

;Microsoft Outlook


[POP3 Incoming]

client = yes

accept =

connect = outlook.office365.com:995

verifyChain = yes

CAfile = ca-certs.pem

checkHost = outlook.office365.com

OCSPaia = yes



I won't bother showing the log for the working machine, but it has the same
config.  I'm really hoping there is simply something missing from the
Windows install.  A coworker has the same problem on their fresh company
provided Win10 install.  My functioning Win10 pc is my personal machine.




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