what is exact dig command you're giving? looks like your returning glue because you're invoking recursion and it's going outside to get the external records. turn recursion off, to start with, on your internal dns server. refresh your zones, or restart your dns server and *make sure you increment the SOA id each zone change*, to make sure your zone changes have been picked up.
you have to get your internal dns server returning your internal IP for mail.jzeller.com before proceeding further.
also i think you're getting confused between hostname and domainname. hostname is your fqdn, ie 'mail.jzeller.com'. domainname is the zone (this is simplification, before anyone starts getting pedantic
, ie 'jzeller.com'. your mx record should be tied to the domainname, not the hostname, so in the zimbra installer you give the Domain 'jzeller.com', not 'mail.jzeller.com' - then it should be able to look up the MX record more correctly.