There are many classes available for use with the K command and for use in rewriting rules. Some require special compile flags to be included when sendmail is built.
Uses Berkeley's db form of database. Database file names have a .db appended (see §33.8.1).
Looks up the best MX record for a host (see §33.8.2).
Uses the ndbm form of database. The database is formed of two files, one whose name ends in .pag and the other in .dir (see §33.8.3).
Removes quotation marks (see §33.8.4).
Uses Berkeley's db form of database (see §33.8.5).
Uses MIT network user authentication services (see §33.8.6).
Uses an internal table to store and look up hostnames (see §33.4.3).
Searches for an aliases database file (see §33.8.8).
Uses the Lightweight Directory Access Protocol (see §33.8.9).
Uses NeXT Computer's network information services (see §33.8.10).
Uses Sun's Network Information Services (nis, see §33.8.11).
Uses Sun's newer Network Information Services (nisplus, see §33.8.12).
Provides a "never found" service (for internal use only, see §33.8.13).
Runs an external program to look up the key (see §33.8.14).
Searches a series of maps (see §33.8.15).
Loads aliases into the symbol table (internally) (see §33.8.16).
Auto-builds sequences of databases based on service-switch file entries (see §33.8.17).
Looks up keys in flat text files (see §33.8.18).
Uses the User Database (see §33.8.19).
Looks up local passwd(5) information (see §33.8.20).