Quoting Carlos Alberto silverdog@gmail.com:

Hi guys, sorry for bother i'am looking how to fix the passwords with non-ascii characters (like ñ). i'am using dovecot version 1.2.15 on debian.

Thanks in advance.

This has been tested many times, dovecot isn't the issue.

More likely your backend is causing a problem, be it sql, ldap, pam,
or however your storing them.

I know I have personally tested ñ against Windows LDAP and openldap
using dovecot.