Conversion channel

The conversion channel performs arbitrary body-part-by-body-part conversions on messages flowing through the MTA. Any subset of MTA message traffic can be selected for conversion and any set of programs  or command procedures can be used to perform conversion processing. (The MTA&#x27;s native conversion facilities are fairly limited, so the ability to call external converters is crucial.)   A special "database"   (stored as the   MTA option in Unified Configuration, or in the   file in legacy configuration)  is consulted to choose an  appropriate conversion for each body part.

For instance, third party document converters or virus scanning software may be hooked in for automatic execution via the conversion  channel. Or sites may develop their own custom applications to hook in via the conversion channel.

Because the conversion channel is intended for "intermediate" processing of messages, the MTA has a special sort of routing available  for it, whereby messages are routed without affecting the recipient  address(es); see the    mapping table. This special sort of routing used to route messages through the conversion channel without modification to the actual  addresses can also be used for other purposes: to route through third  party channel programs, or to route out to third party spam/virus SMTP  hosts (that will then relay messages back to the MTA). See the discussion of  alternate channel routing via the CONVERSIONS mapping.

See also:
 * CONVERSIONS mapping table
 * conversions MTA Option
 * Conversion channel definition
 * Conversion control
 * Alternate channel routing via the CONVERSIONS mapping
 * Message conversions
 * Channels