SERVFAIL for dig @localhost mydomain3.com. There's nothing in my logs, and mydomain1.com and mydomain2.com work fine.

nsd.md

/etc/nsd.conf

# cd /usr/ports/net/ldns/
# make install clean
#
# cd /etc/nsd/
#
# Generate zone signing key
#
#   ldns-keygen -a RSASHA1_NSEC3 -b 1024 <domain>
#
# Generate key signing key
#
#   ldns-keygen -a RSASHA1_NSEC3 -b 2048 -k <domain>
#
# Sign or re-sign the zone
#
#   ldns-signzone <domain> <zone signing key> <key signing key>
#
# nsdc rebuild
# /etc/rc.d/nsd restart
#

server:
  ip4-only: yes
  hide-version: yes

zone:
  name: "mydomain1.com"
  zonefile: "/etc/nsd/mydomain1.com.signed"
  notify: 222.22.222.22 NOKEY
  provide-xfr: 222.22.222.22 NOKEY

zone:
  name: "mydomain2.com"
  zonefile: "/etc/nsd/mydomain2.com.signed"
  notify: 222.22.222.22 NOKEY
  provide-xfr: 222.22.222.22 NOKEY
  
zone:
  name: "mydomain3.com"
  zonefile: "/etc/nsd/mydomain3.com.signed"
  notify: 222.22.222.22 NOKEY
  provide-xfr: 222.22.222.22 NOKEY
  

WORKING

/etc/nsd/mydomain1.com

$ORIGIN mydomain1.com.

$TTL 3m

@ IN SOA ns.mydomain1.com. billy.mydomain1.com. (

2013070501 1h 15m 1w 3m )

@ NS ns.mydomain1.com.
@ NS ns.myregistrar.com.

@ MX 10 mail.mydomain1.com.

@ A 11.111.11.111

ns IN A 11.111.11.111

mail IN A 11.111.11.111

myhostname IN A 11.111.11.111

www IN CNAME mydomain.com.

WORKING

/etc/nsd/mydomain2.com

$ORIGIN mydomain2.com.

$TTL 3m

@ IN SOA ns.mydomain1.com. billy.mydomain1.com. (

2013061001 1h 15m 1w 3m )

@ NS ns.mydomain1.com.
@ NS ns.myregistrar.com.

@ MX 10 mail.mydomain1.com.

@ A 11.111.11.111

www IN CNAME mydomain2.com.

NOT WORKING

/etc/nsd/mydomain3.com

$ORIGIN mydomain3.com.

$TTL 3m

@ IN SOA ns.mydomain1.com. billy.mydomain1.com. (

2013061001 1h 15m 1w 3m )

@ NS ns.mydomain1.com.
@ NS ns.myregistrar.com.

@ MX 10 mail.mydomain1.com.

@ A 11.111.11.111

www IN CNAME mydomain3.com.