Domain database

The MTA&#x27;s domain database, seldom used nowadays, provided an alternate location for storing rewrite rules, for cases of exceptionally large numbers of rewrite rules.

In early versions of the MTA, the format of the domain database was an on-disk database, built using the   utility  based upon a flat text file input. The allowed format of the flat text input file is: key value one entry per line, with the  beginning in column one, one or more white space (SP or TAB) characters, and then the   on the right hand side.

The  MTA option controls which characters (by default exclamation point and semicolon) in column one of a line are considered to indicate a comment line. The left angle character may be used to read another file into the domain database text input file.

For a  "on disk" database, the left hand side (the key) cannot contain spaces or tabs unless the   switch is used; the maximum length of the key and value depend upon whether the   switch is used.

New in the 8.0 release, the MTA supports use of memcache for certain database/storage uses, including the domain database; see the  MTA option.

The  MTA option controls whether or not the MTA makes use of the domain database. In MS 7.2 and earlier, the default for  was 1, so the mere presence of the domain database file was enough to activate this  database facility in the MTA. As of MS 7.3, the default for  changed to 0 from the prior default of 1, so as of MS 7.3 it is necessary to explicitly set    (and then if using a compiled configuration, recompile the configuration), and restart any long-running processes (e.g., SMTP server processes)  to enable consultation of the domain database. Note that the domain database is consulted only when no match was found among the rules in the  group (Unified Configuration) or  the configuration file (legacy configuration). That is, the domain database is only consulted if a given rule is not found in the  group or configuration file,  so rules can always be added to override those in the database.

See also:
 * crdb utility
 * use_domain_database MTA Option
 * domain_database_url MTA Option
 * comment_chars MTA Option
 * Rewrite rules