33.6 Database Maps and m4

Some databases, such as user , are a part of UNIX. Others are a part of sendmail , like the User Database described above. Many, however, are implemented in rules and rule sets. This latter sort of database is therefore available via the m4 technique. Currently, all m4 available databases are implemented as FEATUREs. Table 33.7 lists those available. The second column shows you where to find information about each.

Table 33.7: Database FEATUREs

Feature		Version	Description
domaintable	Section 19.6.10, FEATURE(domaintable)	V8.1 and above	Accept other domains as equivalent to the local domain
genericstable	Section 19.6.11, FEATURE(genericstable)	V8.8 and above	Transform sender addresses
mailertable	Section 19.6.14, FEATURE(mailertable)	V8.1 and above	Select new delivery agents based on an external database
virtusertable	Section 19.6.28, FEATURE(virtusertable)	V8.8 and above	Support for virtual domains

Note that these FEATUREs do not necessarily need to be used with database files. To illustrate, consider the domaintable feature (see Section 19.6.10 ). It is included in your mc file like this:

FEATURE(`domaintable',`nis domaintable')

Here, we specify that the database is to be an nis map. This causes the key to be looked up via the nis services and any match to be returned the same way.