Mail domain name – If you are setting up NIS as the primary name service, sendmail automatically strips the first component of the NIS domain name and uses the result as the mail domain name. For example, ebs.admin.example.com becomes admin.example.com.
Mail host name – When the DNS forwarding feature is turned on, queries that NIS cannot resolve are forwarded to DNS, so you do not need a mailhost entry in the NIS host map.
Full host names – Although NIS does not “understand” full host names, DNS does understand. This requirement is satisfied when you follow the regular procedure for setting up NIS and DNS.
Matching full host names and short host names – For every host entry in the NIS host table, you must have a corresponding host entry in DNS.
Multiple NIS domains in one mail domain – All NIS host maps under a common mail domain should have the same set of host entries. For example, the host map in the ebs.admin.example.com domain should be the same as the host map in the esg.admin.example.com domain. Otherwise, one address might work in one NIS domain, but fail in the other NIS domain.