This works if I use separate userdb and passdb queries. Does deliver not support the prefetch authentication method?

deliver does not support prefetch. See bottom of page:

http://wiki.dovecot.org/AuthDatabase/LDAP

I have three stanzas in my dovecot.conf

other hosts

passdb ldap { args = /etc/dovecot/dovecot-ldap-domains.conf }

userdb prefetch { }

LDA requires the userdb stanzas

use passdb

userdb ldap { args = /etc/dovecot/dovecot-ldap-domains.conf }

Jim