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I'm attempting to disable SSLv2 support (amongst other things) in Courier on Linux. In /etc/courier/imapd-ssl I have:

TLS_CIPHER_LIST="HIGH:!MEDIUM:!SSLv2:!LOW:!EXP:!aNULL:!ADH:@STRENGTH:!3DES"
TLS_PROTOCOL=TLS1
TLS_STARTTLS_PROTOCOL=TLS1

This works nicely on imaps (993/tcp):

# openssl s_client -connect localhost:995 -ssl2
CONNECTED(00000003)
write:errno=104

But for STARTTLS on 143/tcp it still seems to allow SSLv2:

openssl s_client -connect localhost:143 -starttls imap -ssl2
CONNECTED(00000003)

By contrast:

openssl s_client -connect localhost:143 -starttls imap -ssl3
CONNECTED(00000003)
140692334688072:error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version number:s3_pkt.c:339:
---
no peer certificate available
---
No client certificate CA names sent
---
SSL handshake has read 549 bytes and written 7 bytes
---
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol  : SSLv3
Cipher    : 0000
Session-ID: 
Session-ID-ctx: 
Master-Key: 
Key-Arg   : None
Krb5 Principal: None
PSK identity: None
PSK identity hint: None
Start Time: 1492550234
Timeout   : 7200 (sec)
Verify return code: 0 (ok)
---

So it looks to me is as SSLv2 is still enabled when using STARTTLS on 143

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