[stunnel-users] stunnel not working properly on Redhat linux (fresh install)

Klaus Kloeser klaus at kloeser.com
Fri Jan 4 15:14:27 CET 2019



I have set up Stunnel as SSL Wrapper for googlemail on a Redhat Enterprise Linux 7.2 installation.

The stunnel.conf:

output = /var/log/stunnel.log 

cert = /etc/pki/tls/certs/2019stunnel.pem 

client = yes 

sslVersion = TLSv1 



accept = 1925




lets me start stunned well.

I have created the file 2019stunnel.pem following the Instructions on Redhat:

make 2019stunnel.pem in the correct directory (certs)

now I tried to telnet localhost 1925; I get a “connected”, but nothing more. telnet smtp.googlemail 587 runs very well, I get connected, so I assume it is not a firewall issue.

I checked the options 

sslVersion = TLSv1 and 

sslVersion = all alternatively, which led to different errors in stunnel.log:

Service [ssmtp] accepted connection from 2019.01.04 14:45:01 LOG3[4500:140416608397056]: connect_blocking: connect 2a00:1450:400c:c0c::10:587: Network is unreachable (101) 2019.01.04 14:45:01 LOG5[4500:140416608397056]: connect_blocking: connected 2019.01.04 14:45:01 LOG5[4500:140416608397056]: Service [ssmtp] connected remote server from 2019.01.04 14:45:01 LOG3[4500:140416608397056]: SSL_connect: 140770FC: error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol 2019.01.04 14:45:01 LOG5[4500:140416608397056]: Connection reset: 0 byte(s) sent to SSL, 0 byte(s) sent to socket 2019.01.04 14:54:24 LOG5[4500:140416608249920]: Terminated


Service [ssmtp] accepted connection from 2019.01.04 14:54:36 LOG5[7437:139957105055488]: connect_blocking: connected 2019.01.04 14:54:36 LOG5[7437:139957105055488]: Service [ssmtp] connected remote server from 2019.01.04 14:54:36 LOG3[7437:139957105055488]: SSL_connect: 1408F10B: error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version number 2019.01.04 14:54:36 LOG5[7437:139957105055488]: Connection reset: 0 byte(s) sent to SSL, 0 byte(s) sent to socket

Now Open SSL:

Openssl output:

openssl s_client -connect localhost:1925 CONNECTED(00000003)


no peer certificate available

No client certificate CA names sent

SSL handshake has read 0 bytes and written 289 bytes

New, (NONE), Cipher is (NONE) Secure Renegotiation IS NOT supported Compression: NONE Expansion: NONE No ALPN negotiated SSL-Session: Protocol : TLSv1.2 Cipher : 0000 Session-ID: Session-ID-ctx: Master-Key: Key-Arg : None Krb5 Principal: None PSK identity: None PSK identity hint: None Start Time: 1546610402 Timeout : 300 (sec) Verify return code: 0 (ok)

What do I miss here; what is running wrong ?



Mit freundlichen Grüßen/ best regards


Klaus Klöser


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