Can't login: @-sign in login name

[Admin@bbs1]

Hi,
due to a server change i ported my ldap Accounts to a new host. I tried 
to migrate my cyrus imap settings but i still can't log in, because the 
realm is stripped. For example "info at my-domain.com" becomes simply "info".
I tried to adopt the /etc/sasalauthd.conf but that doesn't seem to 
change anything. I think some parts of the underlying system has changed 
substantially over the years. New OS is CentOS release 6.5 (Final).

/etc/saslauthd.conf:
ldap_servers: ldap://localhost:389/
ldap_scope: sub
ldap_password_attr: userPassword
ldap_default_realm: basichostname.net
ldap_filter: uid=%U@%r
ldap_search_base: dc=my-domain,dc=com

/etc/imapd.conf:
configdirectory: /var/lib/imap
partition-default: /var/spool/imap
admins: cyrus
sievedir: /var/lib/imap/sieve
sendmail: /usr/sbin/sendmail
hashimapspool: true
sasl_pwcheck_method: saslauthd
unixhierarchysep: 1
virtdomains: yes
allowplaintext: yes
sasl_mech_list: DIGEST-MD5 CRAM-MD5 PLAIN LOGIN
tls_cert_file: /etc/pki/cyrus-imapd/cyrus-imapd.pem
tls_key_file: /etc/pki/cyrus-imapd/cyrus-imapd.pem
tls_ca_file: /etc/pki/tls/certs/ca-bundle.crt
autocreatequota: 12048000

Can anybody give me any helpful hints?

Thank's a lot in advance
Malte