bad protocol error Testing SASL configuration

15 msg	Header for message size?
3 msg	address rewriting
2 msg	address_verify_relayhost and relay_domains
5 msg	pflogsumm reports
11 msg	Changing Queue IDs
3 msg	another authentication failure( with sasl)
2 msg	Bypass Spam checks for certain destinations
11 msg	Postfix 'too nice' with content_filter
7 msg	profiling a milter (dkim in particular)
7 msg	spammers tacking on headers how to block?
7 msg	[Fwd: Re: RFC 821]
1 msg	Re:
4 msg	(No Subject)
2 msg	RFC 821
7 msg	Suspending mail delievery to a specific user
2 msg	Re: OT - massive newsletter
12 msg	List management issue: possibly Off Topic

bad protocol error Testing SASL configuration
\ Alessia Moretti (19 Sep 2007)
. \ Patrick Ben Koetter (19 Sep 2007)

2 msg	warning: smtpd_sasl_auth_enable is true, but SA...
1 msg	Quota Problem

Subject:	bad protocol error Testing SASL configuration
Group:	Postfix-users
From:	Alessia Moretti
Date:	19 Sep 2007

Hallo evryone

I'm really new of the email-world but I found it very inetersting.
I'm doing a stage for my degree and my goal is to install a working mail
server using postfix-amavisd-clamd-Sasl and Cyrus-Imap.
After the configuration I'm testing the authentication mechanism used by
SASL.
I've started a Telent session and at the moment to autenticate myself I
wrote
AUTH PLAIN xxxxxxxxxxx
where xxxxxxxxx is string obtained with the comand
per -MMIME::Base64 -e \ 'print
encode_base64("useraddress\0useraddress\0password).

The authentication fail and I obtain this answer

435 4.7.0 Error: authentication failed: authentication failure

Where would I search first to fixn the problem? Where would most probably be
the config error?
Thanks to everyone
any suggestion will be appreciate
Alessia