Message conversions

There are two broad categories of message conversions in the MTA, controlled by two corresponding  mapping tables and the MTA. In Unified Configuration, the mappings are stored under the  MTA option group,  and the MTA conversion entries are stored under the    MTA option; in legacy configuration, the MTA mapping tables are stored in the    file, and the MTA conversion entries are stored in the    file.

The first category of message conversion is that of character set, formatting, and labelling conversions performed internally by the MTA. The application of such conversions is controlled by the     mapping table. effects are discussed in Character set conversion and message reformatting.

The second category of message conversion is that of conversion of message attachments using  external, third-party programs and site-supplied procedures, such as  document converters. The application of such conversions is controlled by the    mapping table,  and messages requiring such  conversions are thereby routed through the MTA&#x27;s    channel; the  conversion channel executes the site-specified external conversion  procedures.

Note that the MTA   entries (stored in the   file in legacy configuration),  are used to  specify the details of   mapping table  triggered external conversions  and to specify the details of some internal     mapping table  triggered conversions.

The    utility can perform character set conversions for testing or scripting purposes; the   utility can perform certain message conversions, for testing purposes.

Note that certain basic choices regarding the fundamental handling of attachments/MIME parts can be configured for arbitrary channels via setting of channel options, potentially not requiring any of the more complex conversion channel or message reformatting facilities discussed here; for these basic choices,   see the Attachments and MIME processing channel options.

See also:
 * Conversion channel
 * Conversion tags
 * conversions MTA Option
 * conversion_size MTA Option
 * Character set conversion and message reformatting
 * Mapping tables
 * The mapping group
 * CONVERSIONS mapping table
 * CHARSET-CONVERSION mapping table
 * Interactions between conversions and character set conversions
 * test -translation utility
 * test -mime utility
 * Attachments and MIME processing channel options
 * The MTA