Because NIS+ can have a domain hierarchy while NIS has a flat domain space, changing to NIS+ can have effects on your mail environment. With NIS, only one mail host is required. If you use a domain hierarchy for NIS+, you may need one mail host for each domain in the namespace because names in separate domains may be no longer unique.
Therefore, the email addresses of clients who are not in the root domain may change. As a general rule, client email addresses can change when domain names change or when new levels are added to the hierarchy.
In earlier Solaris releases, these changes required a great deal of work. This release provided several sendmail enhancements to make the task easier. In addition, NIS+ provides a sendmailvars table. The sendmail program first looks at the sendmailvars table (see Table 2-5), then examines the local sendmail.cf file.
Be sure that mail servers reside in the NIS+ domain whose clients they support. For performance reasons, do not use paths to direct mail servers to tables in other domains.