[Dovecot] Problem with LDAP and Dovecot

[Peter Clark]

    I am trying to set up Dovecot so that it uses LDAP, but I keep getting 
this error message in /var/log/syslog:

Dec 12 03:38:17 mydomain dovecot-auth: LDAP: ldap_search() failed (filter 
user_filter = (mail=user at mydomain.tld)): Bad search filter

Relevant configuration files:
/etc/dovecot-ldap.conf:
hosts = localhost
dn = cn=dovecot,ou=sysAccounts,dc=mydomain,dc=tld
dnpass = password
ldap_version = 3
base = ou=mailAccounts,dc=mydomain,dc=tld
deref = never
scope = subtree
user_attrs = mail,,,,,
user_filter = (mail=%u)
pass_attrs = mail,userPassword
pass_filter = user_filter = (mail=%u)
default_pass_scheme = CRYPT
user_global_uid = 5000
user_global_gid = 5000

/etc/dovecot.conf:
protocols =  imap imaps pop3s
imap_listen = 127.0.0.1
imaps_listen = *
pop3s_listen = *
ssl_cert_file = /etc/ssl/mydomain.tld/Cert.pem
ssl_key_file = /etc/ssl/mydomain.tld/PrivateKey.pem
disable_plaintext_auth = yes
login = imap
login_user = dovecot
login = pop3
verbose_proctitle = yes
first_valid_uid = 5000
last_valid_uid = 5000
first_valid_gid = 5000
last_valid_gid = 5000
mail_extra_groups = mail
valid_chroot_dirs = /var/mail/virtualmail
default_mail_env = maildir:/var/mail/virtualmail/%n/Maildir
auth = default
auth_mechanisms = plain
auth_userdb = ldap /etc/dovecot-ldap.conf
auth_passdb = ldap /etc/dovecot-ldap.conf
auth_user = dovecot
auth_verbose = yes
auth_debug = no

In /etc/ldap/slapd.conf:
access to attribute=userPassword
        by dn="cn=admin,dc=mydomain,dc=tld" write
        by dn="cn=dovecot,ou=sysAccounts,dc=mydomain,dc=tld" read
        by anonymous auth
        by self write
        by * none

Output of 'slapcat | grep dovecot':
dn: cn=dovecot,ou=sysAccounts,dc=mydomain,dc=tld
cn: dovecot
sn: dovecot

    I've even tried changing the dn to admin, but I still get the same error. 
What am I doing wrong?
    :Peter