SASL, LDAP and virtual domains

[AJ]

Trying to set up both saslauthd and cyrus-imapd for virtual domain support.
I would like to authenticate against the LDAP mail attribute, so I use 
this in saslauthd.conf:

ldap_filer: mail=%U@%d

This does not work, however, but if I have a uid attribute set in ldap 
in the form of:  john.smith at domain.com, authentication works.

Is it possible to use the mail attribute to authenticate, as opposed to 
the uid attribute?  Do I have the wrong ldap_filter?

Thanks.
AJ

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