Hi Graham, I was unable to reproduce this issue. I don't have a Windows 7 machine to test, but it should be no difference with Windows 10 or 11. Can you try updating your [Zen-pop3] config like this: ? [zen-pop3] client = yes accept = 127.0.0.1:110 connect = mailhost.zen.co.uk:995 CAfile = ca-certs.pem verifyChain = yes checkHost = mailhost.zen.co.uk OCSPaia = yes You can also set debug=5 instead of commenting the line to have the same level log of verbosity. Let us know how it goes. Thanks. Regards,Jose On Thursday, May 14, 2026 at 08:09:03 AM GMT-5, Graham Jones via stunnel-users <stunnel-users@lists.stunnel.org> wrote: I'm new to stunnel. stunnel 5.78 on x64-pc-mingw32-gnu platform Windows 7 Pro Using Outlook to open a connection to a POP server Extract from stunnel.conf [Zen-pop3] client = yes accept = 127.0.0.1:110 connect = mailhost.zen.co.uk:995 CAfile = ca-certs.pem With debug = 7 the test succeeds. The log shows: 2026.05.13 16:49:06 LOG5[4]: Service [Zen-pop3] accepted connection from 127.0.0.1:49596 2026.05.13 16:49:06 LOG5[4]: s_connect: connected 212.23.1.19:995 2026.05.13 16:49:06 LOG5[4]: Service [Zen-pop3] connected remote server from 127.0.0.1:49598 2026.05.13 16:49:06 LOG5[4]: Connection closed: 59 byte(s) sent to TLS, 202 byte(s) sent to socket With ;debug a test connection fails after about 20 seconds delay. Log extract: 2026.05.13 17:22:05 LOG5[6]: Service [Zen-pop3] accepted connection from 127.0.0.1:53162 2026.05.13 17:22:05 LOG5[6]: s_connect: connected 212.23.1.11:995 2026.05.13 17:22:05 LOG5[6]: Service [Zen-pop3] connected remote server from 127.0.0.1:53163 2026.05.13 17:22:26 LOG3[6]: SSL_connect: Connection reset by peer (WSAECONNRESET) (10054) Why does it only work with debug enabled? Any ideas, please? Regards, == Graham _______________________________________________ stunnel-users mailing list -- stunnel-users@lists.stunnel.org To unsubscribe send an email to stunnel-users-leave@lists.stunnel.org