Conversion tags

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The MTA has a private mechanism of conversion tags. Conversion tags may be set and used in a variety of ways and for a variety of purposes; besides the original use for triggering user-specific automatic documention conversion, another common use is for causing or influencing special routing of messages.

Note that conversion tags are stored in a private-to-the-MTA field in the message envelope; they are not visible in received messages. (However, message conversion tags present on messages transitting the MTA will be included in MTA message transaction log entries if the log_conversion_tag MTA option is enabled.)

Conversion tags may be added via channel options, (sourceconversiontag, destinationconversiontag, deliveryflags), via LDAP attributes (ldap_source_conversion_tag, ldap_conversion_tag, ldap_domain_attr_source_conversion_tag, ldap_domain_attr_conversion_tag), via an alias option (alias_conversion_tag) or [CONVERSION_TAG] alias file named parameter, via recipient access mapping tables or the FROM_ACCESS mapping table, or via the Sieve conversiontag extensions. Conversion tags present on a message may influence certain mapping table operations (CONVERSIONS mapping table, CHARSET-CONVERSION mapping table, MESSAGE-SAVE-COPY mapping table when selected via message_save_copy_flags, as well as various address mapping tables as controlled by the include_conversiontag MTA option), and control matching and hence application of specific conversions entries. Complex effects due to, and manipulations of, conversion tags are also possible via Sieve conversiontag extensions.

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