The K command is used to declare a database support in the configuration file:
name class switches database
The name is the symbolic name used in rule sets with the $( and $) operators. The class is described in the next section. The switches are described immediately below. The database is either the name of an external database (possibly created with makemap), or that of a flat text file (see §33.3).
Appends values for duplicate keys (see §126.96.36.199).
Appends tag on a successful match (see §188.8.131.52).
Prevents folding of keys to lowercase prior to the lookup (see §184.108.40.206).
Specifies the column for the key in flat text or some network files (see §220.127.116.11).
Suppresses replacement on match (see §18.104.22.168).
Appends a null byte to the key before the lookup (see §22.214.171.124).
Causes sendmail to not add a null byte to the key before the lookup. Note that with neither -O nor -N, sendmail determines adaptively whether or not it should add a null byte (see §126.96.36.199).
Specifies that the existence of the database file is optional (see §188.8.131.52).
Prevents quotes from being stripped from the key before the lookup (see §184.108.40.206).
Specifies the space replacement character (see §220.127.116.11).
Specifies the value's column for flat or some network files (see §18.104.22.168).
Specifies the column delimiter for flat or some network files (see §22.214.171.124).