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 freezes: 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) from 127.0.0.1:51378 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 from 127.0.0.1:51378 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 52.96.24.210:995 2019.05.21 22:50:19 LOG7[2]: s_connect: s_poll_wait 52.96.24.210:995: 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. [WQBRAFgAUABSADAAMQBDAEEAMAAwA DgANgAuAEMAQQBOAFAAUgBEADAAMQAuAFAAUgBPAEQALgBPAFUAVABMAE8ATwBLAC4AQwBPAE0A] user LoadAccept@example.com +OK pass LAxxxxxx +OK User successfully logged on. list +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 = 127.0.0.1:110 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. Thanks, Mario --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus