Setting Up sendmail Requirements for Name Services

sendmail imposes various requirements on name services. This section explains these requirements and how to satisfy them. For more information, refer to the in.named(1M), nis+(1), nisaddent(1M), and nsswitch.conf(4) man pages.

Establishing the Mail Domain Name With a Name Service

The mail domain name must be a suffix of the name service domain. For example, if the domain name of the name service is A.B.C.D, the mail domain name could be one of the following:

• A.B.C.D

• B.C.D

• C.D

• D

When first established, the mail domain name is often identical to the name service domain. As the network grows larger, the name service domain can be divided into smaller pieces to make the name service more manageable. However, the mail domain often remains undivided to provide consistent aliasing.

Host Name Space Data

The host table or map in the name service must be set up to support three types of gethostbyname() queries:

• mailhost - Some name service configurations satisfy this requirement automatically.

• Full host name (for example, smith.admin.acme.com) - Many name service configurations satisfy this requirement.

• Short host name (for example, smith) - sendmail must connect to the mail host to forward external mail. To determine if a mail address is within the current mail domain, gethostbyname() is invoked with the full host name. If the entry is found, the address is considered internal.

  NIS, NIS+, and DNS all support gethostbyname() with a short host name as an argument, so this requirement is automatically satisfied.

Two additional rules about the host name space need to be followed to establish the sendmail services within a name space properly.

1. gethostbyname() with full and short host name should yield consistent results. For example, gethostbyname(smith.admin.acme.com) should return the same result as gethostbyname(smith), as long as both functions are called from the mail domain admin.acme.com.

2. For all name service domains under a common mail domain, gethostbyname() with a short host name should yield the same result. For example, given the mail domain smith.admin.acme.com, gethostbyname(smith) should return the same result calling from either domain ebb.admin.acme.com or esg.admin.acme.com. The mail domain name is usually shorter than the name service domain, giving this requirement special implications for various name services.