problem with STARTTLS on port 143 after upgrade to 3.12 with openssl 3.6

Hi,

After upgrade from 3.10.0-1 -> 3.12.1-1 using ArchLinux AUR build[2] STARTTLS on port 143 stopped to work. Using openssl I see "This TLS version forbids renegotiation."

Current openssl version on Arch is 3.6.0.

changelog.md[1]:

"Client-initiated renegotiation is disabled by default. To allow it, use the -client_renegotiation option, the SSL_OP_ALLOW_CLIENT_RENEGOTIATION flag, or the "ClientRenegotiation" config parameter as appropriate."

Output from openssl test:

[zork@serenity ~]$ openssl s_client -starttls imap -crlf -connect 'zork.pl:143'
Connecting to 178.32.202.57
CONNECTED(00000003)
Didn't find STARTTLS in server response, trying anyway...
80BBE3D7E87F0000:error:0A00010B:SSL routines:tls_validate_record_header:wrong version number:ssl/record/methods/tlsany_meth.c:84:
---
no peer certificate available
---
No client certificate CA names sent
Negotiated TLS1.3 group: <NULL>
---
SSL handshake has read 1253 bytes and written 1566 bytes
Verification: OK
---
New, (NONE), Cipher is (NONE)
Protocol: TLSv1.3
This TLS version forbids renegotiation.
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)


And for TLS 1.2:

[zork@serenity ~]$ openssl s_client -starttls imap -crlf -connect 'zork.pl:143' -tls1_2
Connecting to 178.32.202.57
CONNECTED(00000003)
Didn't find STARTTLS in server response, trying anyway...
802BB19E427F0000:error:0A00010B:SSL routines:tls_validate_record_header:wrong version number:ssl/record/methods/tlsany_meth.c:84:
---
no peer certificate available
---
No client certificate CA names sent
---
SSL handshake has read 1253 bytes and written 233 bytes
Verification: OK
---
New, (NONE), Cipher is (NONE)
Protocol: TLSv1.2
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:
     PSK identity: None
     PSK identity hint: None
     SRP username: None
     Start Time: 1761042230
     Timeout   : 7200 (sec)
     Verify return code: 0 (ok)
     Extended master secret: no
---


I am not sure what to do now. Is imap:143 + STARTTLS now considered insecure? should I reconfigure all mail clients to use imaps instead or imap+STARTTLS?
This is very small setup and I do not need to support STARTTLS on port 143.

Regards,
Łukasz

[1] https://github.com/openssl/openssl/blob/master/CHANGES.md#openssl-36
[2] https://aur.archlinux.org/packages/cyrus-imapd

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