I'm using the latest Stunnel (5.35), running under Windows Server 2000, to download emails from Outlook(Office365)/Outlook 2016 to another email client called OfficeTalk which only supports unencrypted POP3, so it can't access Outlook directly.

First problem is that although most emails are downloaded without problem, some stubbornly and consistently refuse to be downloaded. This omission doesn't seem related to attachments, encoding, size, date, or anything else that I can see. Has anyone else experienced this or have any idea why it might be happening??

Second problem is that the first download doesn't produce anything, but if I run the request again, it works - the only difference in the log files is the IP addresses

I'd greatly appreciate any advice on this - I've checked the threads but can't find anything similar.

Many thanks in advance

Martin

Config file for all attempts is:

debug=7
output = c:\program files\stunnel\stunnel.log

[outlook-pop3]
client = yes
accept = 127.0.0.1:110
connect = outlook.office365.com:995

Logfile for successful download of one email is:

12:49:50 LOG7[cron]: Cron thread initialized

12:49:50 LOG7[main]: Running on Windows 5.0

12:49:50 LOG7[main]: No limit detected for the number of clients

12:49:50 LOG5[main]: stunnel 5.35 on x86-pc-msvc-1500 platform

12:49:50 LOG5[main]: Compiled/running with OpenSSL 1.0.2h-fips 3 May 2016

12:49:50 LOG5[main]: Threading:WIN32 Sockets:SELECT,IPv4 TLS:ENGINE,FIPS,OCSP,PSK,SNI

12:49:50 LOG7[main]: errno: (*_errno())

12:49:50 LOG7[ui]: GUI message loop initialized

12:49:50 LOG7[main]: Running on Windows 5.0

12:49:50 LOG5[main]: Reading configuration from file stunnel.conf

12:49:50 LOG5[main]: UTF-8 byte order mark detected

12:49:50 LOG5[main]: FIPS mode disabled

12:49:50 LOG7[main]: Compression disabled

12:49:50 LOG7[main]: Snagged 64 random bytes from C:/.rnd

12:49:50 LOG7[main]: Wrote 1024 new random bytes to C:/.rnd

12:49:50 LOG7[main]: PRNG seeded successfully

12:49:50 LOG6[main]: Initializing service [outlook-pop3]

12:49:50 LOG7[main]: No certificate or private key specified

12:49:50 LOG4[main]: Service [outlook-pop3] needs authentication to prevent MITM attacks

12:49:50 LOG7[main]: SSL options: 0x03000004 (+0x03000000, -0x00000000)

12:49:50 LOG5[main]: Configuration successful

12:49:50 LOG7[main]: Listening file descriptor created (FD=344)

12:49:50 LOG7[main]: Service [outlook-pop3] (FD=344) bound to 127.0.0.1:110

12:49:53 LOG7[main]: Found 1 ready file descriptor(s)

12:49:53 LOG7[main]: FD=204 ifds=r-x ofds=---

12:49:53 LOG7[main]: Service [outlook-pop3] accepted (FD=356) from 127.0.0.1:3801

12:49:53 LOG7[main]: Creating a new thread

12:49:53 LOG7[main]: New thread created

12:49:53 LOG7[0]: Service [outlook-pop3] started

12:49:53 LOG7[0]: Option TCP_NODELAY set on local socket

12:49:53 LOG5[0]: Service [outlook-pop3] accepted connection from 127.0.0.1:3801

12:49:53 LOG6[0]: failover: round-robin, starting at entry #1

12:49:53 LOG6[0]: s_connect: connecting 132.245.224.162:995

12:49:53 LOG7[0]: s_connect: s_poll_wait 132.245.224.162:995: waiting 10 seconds

12:49:53 LOG5[0]: s_connect: connected 132.245.224.162:995

12:49:53 LOG5[0]: Service [outlook-pop3] connected remote server from 192.168.15.102:3802

12:49:53 LOG7[0]: Option TCP_NODELAY set on remote socket

12:49:53 LOG7[0]: Remote descriptor (FD=380) initialized

12:49:53 LOG6[0]: SNI: sending servername: outlook.office365.com

12:49:53 LOG6[0]: Peer certificate not required

12:49:53 LOG7[0]: SSL state (connect): before/connect initialization

12:49:53 LOG7[0]: SSL state (connect): SSLv2/v3 write client hello A

12:49:53 LOG7[0]: SSL state (connect): SSLv3 read server hello A

12:49:53 LOG6[0]: Certificate verification disabled

12:49:53 LOG7[0]: SSL state (connect): SSLv3 read server certificate A

12:49:53 LOG7[0]: SSL state (connect): SSLv3 read server key exchange A

12:49:53 LOG6[0]: Client certificate not requested

12:49:53 LOG7[0]: SSL state (connect): SSLv3 read server done A

12:49:53 LOG7[0]: SSL state (connect): SSLv3 write client key exchange A

12:49:53 LOG7[0]: SSL state (connect): SSLv3 write change cipher spec A

12:49:53 LOG7[0]: SSL state (connect): SSLv3 write finished A

12:49:53 LOG7[0]: SSL state (connect): SSLv3 flush data

12:49:53 LOG7[0]: SSL state (connect): SSLv3 read finished A

12:49:53 LOG7[0]: 1 client connect(s) requested

12:49:53 LOG7[0]: 1 client connect(s) succeeded

12:49:53 LOG7[0]: 0 client renegotiation(s) requested

12:49:53 LOG7[0]: 0 session reuse(s)

12:49:53 LOG6[0]: SSL connected: new session negotiated

12:49:53 LOG7[0]: Peer certificate was cached (4882 bytes)

12:49:53 LOG6[0]: Negotiated TLSv1.2 ciphersuite ECDHE-RSA-AES256-SHA384 (256-bit encryption)

12:49:53 LOG7[0]: Compression: null, expansion: null

12:49:54 LOG6[0]: Read socket closed (readsocket)

12:49:54 LOG7[0]: Sending close_notify alert

12:49:54 LOG7[0]: SSL alert (write): warning: close notify

12:49:54 LOG6[0]: SSL_shutdown successfully sent close_notify alert

12:49:54 LOG7[main]: Found 1 ready file descriptor(s)

12:49:54 LOG7[main]: FD=204 ifds=r-x ofds=---

12:49:54 LOG7[main]: Service [outlook-pop3] accepted (FD=404) from 127.0.0.1:3803

12:49:54 LOG7[main]: Creating a new thread

12:49:54 LOG7[main]: New thread created

12:49:54 LOG7[1]: Service [outlook-pop3] started

12:49:54 LOG7[1]: Option TCP_NODELAY set on local socket

12:49:54 LOG5[1]: Service [outlook-pop3] accepted connection from 127.0.0.1:3803

12:49:54 LOG6[1]: failover: round-robin, starting at entry #2

12:49:54 LOG6[1]: s_connect: connecting 132.245.212.98:995

12:49:54 LOG7[1]: s_connect: s_poll_wait 132.245.212.98:995: waiting 10 seconds

12:49:54 LOG6[0]: SSL socket closed (SSL_read)

12:49:54 LOG7[0]: Sent socket write shutdown

12:49:54 LOG5[0]: Connection closed: 67 byte(s) sent to SSL, 11900 byte(s) sent to socket

12:49:54 LOG7[0]: Remote descriptor (FD=380) closed

12:49:54 LOG7[0]: Local descriptor (FD=356) closed

12:49:54 LOG7[0]: Service [outlook-pop3] finished (1 left)

12:49:54 LOG5[1]: s_connect: connected 132.245.212.98:995

12:49:54 LOG5[1]: Service [outlook-pop3] connected remote server from 192.168.15.102:3804

12:49:54 LOG7[1]: Option TCP_NODELAY set on remote socket

12:49:54 LOG7[1]: Remote descriptor (FD=428) initialized

12:49:54 LOG6[1]: SNI: sending servername: outlook.office365.com

12:49:54 LOG6[1]: Peer certificate not required

12:49:54 LOG7[1]: SSL state (connect): before/connect initialization

12:49:54 LOG7[1]: SSL state (connect): SSLv3 write client hello A

12:49:54 LOG7[1]: SSL state (connect): SSLv3 read server hello A

12:49:54 LOG6[1]: Certificate verification disabled

12:49:54 LOG7[1]: SSL state (connect): SSLv3 read server certificate A

12:49:54 LOG7[1]: SSL state (connect): SSLv3 read server key exchange A

12:49:54 LOG6[1]: Client certificate not requested

12:49:54 LOG7[1]: SSL state (connect): SSLv3 read server done A

12:49:54 LOG7[1]: SSL state (connect): SSLv3 write client key exchange A

12:49:54 LOG7[1]: SSL state (connect): SSLv3 write change cipher spec A

12:49:54 LOG7[1]: SSL state (connect): SSLv3 write finished A

12:49:54 LOG7[1]: SSL state (connect): SSLv3 flush data

12:49:54 LOG7[1]: SSL state (connect): SSLv3 read finished A

12:49:54 LOG7[1]: 2 client connect(s) requested

12:49:54 LOG7[1]: 2 client connect(s) succeeded

12:49:54 LOG7[1]: 0 client renegotiation(s) requested

12:49:54 LOG7[1]: 0 session reuse(s)

12:49:54 LOG6[1]: SSL connected: new session negotiated

12:49:54 LOG7[1]: Deallocating application specific data for addr index

12:49:54 LOG6[1]: Negotiated TLSv1.2 ciphersuite ECDHE-RSA-AES256-SHA384 (256-bit encryption)

12:49:54 LOG7[1]: Compression: null, expansion: null

12:49:56 LOG6[1]: Read socket closed (readsocket)

12:49:56 LOG7[1]: Sending close_notify alert

12:49:56 LOG7[1]: SSL alert (write): warning: close notify

12:49:56 LOG6[1]: SSL_shutdown successfully sent close_notify alert

12:49:56 LOG6[1]: SSL socket closed (SSL_read)

12:49:56 LOG7[1]: Sent socket write shutdown

12:49:56 LOG5[1]: Connection closed: 67 byte(s) sent to SSL, 11884 byte(s) sent to socket

12:49:56 LOG7[1]: Remote descriptor (FD=428) closed

12:49:56 LOG7[1]: Local descriptor (FD=404) closed

12:49:56 LOG7[1]: Service [outlook-pop3] finished (0 left)