problem with auth_rimap between linux and freebsd

[Ombretta Pinazza]

Hello,
I'm trying to configure a linux box as secondary MX server with postfix, 
TLS and SMTPAUTH, where the users should authenticate using their 
credentials on a FreeBSD server runnig cyrus IMAP.

The server is authenticating correctly, but the client does not 
understand, breaking the string "server" in "rver":
     auth_rimap: unexpected response to auth request: rver ready


Configuration of the FreeBSD server:
/usr/local/etc/imapd.conf:
    sasl_pwcheck_method: saslauthd
    sasl_mech_list: plain login


 From a FreeBSD client I can successfully log in using:
bsdclient> saslauthd -a rimap -O x.x.x.x
bsdclient> testsaslauthd -u myusername -p mypassw -f 
/var/state/saslauthd/mux
0: OK "Success."

On the server the log line is:
Apr  8 11:37:46 bsdserver imap[52745]: login: bsdclient [bsd-client-ip] 
myusername plaintext User logged in


But the same test from the linux host fails:

linux> saslauthd -a rimap -O x.x.x.x
linux> testsaslauthd -u myusername -p mypassw -f /var/run/saslauthd/mux
0: NO "authentication failed"

linux> tail /var/log/messages
Apr  8 11:40:25 linuxclient saslauthd[18932]: auth_rimap: unexpected 
response to auth request: rver ready
Apr  8 11:40:25 linuxclient saslauthd[18932]: do_auth         : auth 
failure: [user=username] [service=imap] [realm=] [mech=rimap] 
[reason=[ALERT] Unexpected response from remote authentication server]

On the server side, this login is successful
Apr  8 11:42:08 bsdserver imap[36862]: login: linuxclient 
[linux-client-ip] myusername plaintext User logged in

The cyrus-sasl versions are 2.1.22-4 on linux and 2.1.22 on FreeBSD.

Any hint?
Thank you,
     Ombretta