== Indexing arbitrary mail headers

By default the Recoll mail handler only processes a subset of email headers
(+From+, +To+, +Cc+, +Date+, +Subject+). It is possible to index additional
headers by specifying them inside the 'fields' configuration file, inside
the configuration directory (typically '~/.recoll/').

Lengthy explanations are not really needed here, and I'll just show an
example (duplicated from the configuration section of the manual):

----
[prefixes]
# Index mailmytag contents (with the given prefix)
mailmytag = XMTAG

[stored]
# Store mailmytag inside the document data record (so that it can be
# displayed - as %(mailmytag) - in result lists).
mailmytag = 

[mail]
# Extract the X-My-Tag mail header, and use it internally with the
# mailmytag field name
x-my-tag = mailmytag

----

Limitations:

- The mail filter will only process the first instance for a header
  occurring several times.
- No decoding will take place (ie for non-ascii headers which would have
  some kind of encoding).