=encoding utf8

=head1 NAME

Mail::Message::Head::Partial - subset of header information of a message

=head1 INHERITANCE

 Mail::Message::Head::Partial
   is a Mail::Message::Head::Complete
   is a Mail::Message::Head
   is a Mail::Reporter

=head1 SYNOPSIS

  my $partial = $head->strip;
  $partial->isa('Mail::Message::Head')  # true
  $partial->isDelayed                   # false
  $partial->isPartial                   # true

  $partial->removeFields( qr/^X-/ );
  $partial->removeFieldsExcept( qw/To From/ );
  $partial->removeResentGroups;
  $partial->removeListGroup;
  $partial->removeSpamGroups;

=head1 DESCRIPTION

Header information consumes a considerable amount of memory.  Most of this
information is only useful during a short period of time in your program,
or sometimes it is not used at all.  You then can decide to remove most
of the header information.  However, be warned that it will be lost
permanently: the header (and therefore the message) gets mutulated!

Extends L<"DESCRIPTION" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"DESCRIPTION">.

=head1 OVERLOADED

Extends L<"OVERLOADED" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"OVERLOADED">.

=over 4

=item overload: B<""> stringifaction

Inherited, see L<Mail::Message::Head/"OVERLOADED">

=item overload: B<bool> true/false

Inherited, see L<Mail::Message::Head/"OVERLOADED">

=back

=head1 METHODS

Extends L<"METHODS" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"METHODS">.

=head2 Constructors

Extends L<"Constructors" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Constructors">.

=over 4

=item $class-E<gt>B<build>( [PAIR|$field], ... )

Inherited, see L<Mail::Message::Head::Complete/"Constructors">

=item $obj-E<gt>B<clone>( [@names|ARRAY|Regexps] )

Inherited, see L<Mail::Message::Head::Complete/"Constructors">

=item $class-E<gt>B<new>(%options)

Inherited, see L<Mail::Message::Head/"Constructors">

=back

=head2 Attributes

Extends L<"Attributes" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Attributes">.

=head2 The header

Extends L<"The header" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"The header">.

=over 4

=item $obj-E<gt>B<isDelayed>()

Inherited, see L<Mail::Message::Head/"The header">

=item $obj-E<gt>B<isEmpty>()

Inherited, see L<Mail::Message::Head/"The header">

=item $obj-E<gt>B<isModified>()

Inherited, see L<Mail::Message::Head/"The header">

=item $obj-E<gt>B<knownNames>()

Inherited, see L<Mail::Message::Head/"The header">

=item $obj-E<gt>B<message>( [$message] )

Inherited, see L<Mail::Message::Head/"The header">

=item $obj-E<gt>B<modified>( [BOOLEAN] )

Inherited, see L<Mail::Message::Head/"The header">

=item $obj-E<gt>B<nrLines>()

Inherited, see L<Mail::Message::Head::Complete/"The header">

=item $obj-E<gt>B<orderedFields>()

Inherited, see L<Mail::Message::Head/"The header">

=item $obj-E<gt>B<size>()

Inherited, see L<Mail::Message::Head::Complete/"The header">

=item $obj-E<gt>B<wrap>($integer)

Inherited, see L<Mail::Message::Head::Complete/"The header">

=back

=head2 Access to the header

Extends L<"Access to the header" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Access to the header">.

=over 4

=item $obj-E<gt>B<add>( $field | $line | <$name, $body, [$attrs]> )

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<addListGroup>($object)

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<addResentGroup>($resent_group|$data)

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<addSpamGroup>($object)

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<cleanupOrderedFields>()

The header maintains a list of fields which are ordered in sequence of
definition.  It is required to maintain the header order to keep the
related fields of resent groups together.  The fields are also included
in a hash, sorted on their name for fast access.

The references to field objects in the hash are real, those in the ordered
list are weak.  So when field objects are removed from the hash, their
references in the ordered list are automagically C<undef>'d.

When many fields are removed, for instance with L<removeFields()|Mail::Message::Head::Partial/"Access to the header"> or
L<removeFieldsExcept()|Mail::Message::Head::Partial/"Access to the header">, then it is useful to remove the list of undefs
from the ordered list as well.  In those cases, this method is called
automatically, however you may have your own reasons to call this method.

=item $obj-E<gt>B<count>($name)

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<delete>($name)

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<get>( $name, [$index] )

Inherited, see L<Mail::Message::Head/"Access to the header">

=item $obj-E<gt>B<grepNames>( [@names|ARRAY|Regexps] )

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<listGroup>()

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<names>()

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<print>( [$fh] )

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<printSelected>($fh, <STRING|Regexp>, ...)

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<printUndisclosed>( [$fh] )

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<removeContentInfo>()

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<removeField>($field)

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<removeFields>( <STRING|Regexp>, ... )

Remove the fields from the header which are exactly named 'C<STRING>' (case
insensitive) or match the regular expresssion.  Do not forget to add the
'i' modifier to the regexp, because fields are case insensitive.

See also L<removeField()|Mail::Message::Head::Complete/"Access to the header"> which is used to remove one field object from
the header.  The reverse specification can be made with
C<removeFieldsExcept()>.
Improves base, see L<Mail::Message::Head::Complete/"Access to the header">

» example: 

  $head->removeFields('bcc', 'received');
  $head->removeFields( qr/^content-/i );

=item $obj-E<gt>B<removeFieldsExcept>(STRING|Regexp, ...)

Remove all fields from the header which are not equivalent to one of the
specified STRINGs (case-insensitive) and which are not matching one of
the REGular EXPressions.  Do not forget to add the 'i' modifier to the
Regexp, because fields are case insensitive.

See also L<removeField()|Mail::Message::Head::Complete/"Access to the header"> which is used to remove one field object from
the header.  The reverse specification can be made with C<removeFields()>.
Improves base, see L<Mail::Message::Head::Complete/"Access to the header">

» example: 

  $head->removeFieldsExcept('subject', qr/^content-/i );
  $head->removeFieldsExcept( qw/subject to from sender cc/ );

=item $obj-E<gt>B<removeListGroup>()

Removes all header lines which are used to administer mailing lists.
Which fields that are is explained in L<Mail::Message::Head::ListGroup|Mail::Message::Head::ListGroup>.
Returned is the number of removed lines.
Improves base, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<removeResentGroups>()

Removes all header lines which are member of a I<resent group>, which
are explained in L<Mail::Message::Head::ResentGroup|Mail::Message::Head::ResentGroup>.  Returned is the
number of removed lines.

For removing single groups (for instance because you want to keep the
last), use L<Mail::Message::Head::FieldGroup::delete()|Mail::Message::Head::FieldGroup/"The header">.
Improves base, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<removeSpamGroups>()

Removes all header lines which were produced by spam detection and
spam-fighting software.  Which fields that are is explained in
L<Mail::Message::Head::SpamGroup|Mail::Message::Head::SpamGroup>.  Returned is the number of removed lines.
Improves base, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<resentGroups>()

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<reset>($name, @fields)

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<set>( $field | $line | <$name, $body, [$attrs]> )

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<spamDetected>()

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<spamGroups>( [$names] )

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<string>()

Inherited, see L<Mail::Message::Head::Complete/"Access to the header">

=item $obj-E<gt>B<study>( $name, [$index] )

Inherited, see L<Mail::Message::Head/"Access to the header">

=back

=head2 About the body

Extends L<"About the body" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"About the body">.

=over 4

=item $obj-E<gt>B<guessBodySize>()

Inherited, see L<Mail::Message::Head/"About the body">

=item $obj-E<gt>B<guessTimeStamp>()

Inherited, see L<Mail::Message::Head::Complete/"About the body">

=item $obj-E<gt>B<isMultipart>()

Inherited, see L<Mail::Message::Head/"About the body">

=item $obj-E<gt>B<recvstamp>()

Inherited, see L<Mail::Message::Head::Complete/"About the body">

=item $obj-E<gt>B<timestamp>()

Inherited, see L<Mail::Message::Head::Complete/"About the body">

=back

=head2 Internals

Extends L<"Internals" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Internals">.

=over 4

=item $obj-E<gt>B<addNoRealize>($field)

Inherited, see L<Mail::Message::Head/"Internals">

=item $obj-E<gt>B<addOrderedFields>($fields)

Inherited, see L<Mail::Message::Head/"Internals">

=item $obj-E<gt>B<createFromLine>()

Inherited, see L<Mail::Message::Head::Complete/"Internals">

=item $obj-E<gt>B<createMessageId>()

Inherited, see L<Mail::Message::Head::Complete/"Internals">

=item $obj-E<gt>B<fileLocation>()

Inherited, see L<Mail::Message::Head/"Internals">

=item $obj-E<gt>B<load>()

Inherited, see L<Mail::Message::Head/"Internals">

=item $any-E<gt>B<messageIdPrefix>( [$prefix, [$hostname]|CODE] )

Inherited, see L<Mail::Message::Head::Complete/"Internals">

=item $obj-E<gt>B<moveLocation>($distance)

Inherited, see L<Mail::Message::Head/"Internals">

=item $obj-E<gt>B<read>($parser)

Inherited, see L<Mail::Message::Head/"Internals">

=item $obj-E<gt>B<setNoRealize>($field)

Inherited, see L<Mail::Message::Head/"Internals">

=back

=head2 Error handling

Extends L<"Error handling" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Error handling">.

=over 4

=item $obj-E<gt>B<AUTOLOAD>()

Inherited, see L<Mail::Reporter/"Error handling">

=item $obj-E<gt>B<notImplemented>()

Inherited, see L<Mail::Reporter/"Error handling">

=back

=head2 Cleanup

Extends L<"Cleanup" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Cleanup">.

=over 4

=item $obj-E<gt>B<DESTROY>()

Inherited, see L<Mail::Reporter/"Cleanup">

=back

=head1 DETAILS

Extends L<"DETAILS" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"DETAILS">.

=head2 Ordered header fields

Extends L<"Ordered header fields" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Ordered header fields">.

=head2 Head class implementation

Extends L<"Head class implementation" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Head class implementation">.

=head2 Subsets of header fields

Extends L<"Subsets of header fields" in Mail::Message::Head::Complete|Mail::Message::Head::Complete/"Subsets of header fields">.

=head2 Reducing the header size

A message header is very large in memory and quite large on disk, and
therefore a good candidate for size reduction.  One way to reduce the
size is by simply eliminating superfluous header fields.  Each field
requires at least 100 bytes of run-time memory, so this may help!

Before you start playing around with L<removeFields()|Mail::Message::Head::Partial/"Access to the header"> and
L<removeFieldsExcept()|Mail::Message::Head::Partial/"Access to the header">, you may take a look at two large groups
of fields which can be removes as sets: the resent headers and the
mailinglist headers.

Resent headers describe the intermediate steps in the transmission
process for the messages.  After successful delivery, they are rarely
useful.

When you are archiving a mailinglist, it is hardly ever useful to
store a the list administration lines for each message as well.

=head4 » see examples/reduce.pl in distribution

  foreach my $msg ($folder->messages)
  {  $msg->head->removeResentGroups;
     $msg->head->removeResentList;
  }

=head1 DIAGNOSTICS

=over 4

=item Warning: cannot remove field $name from header: not found.

You ask to remove a field which is not known in the header.  Using
L<delete()|Mail::Message::Head::Complete/"Access to the header">, L<reset()|Mail::Message::Head::Complete/"Access to the header">, or L<set()|Mail::Message::Head::Complete/"Access to the header"> to do the job will not result
in warnings: those methods check the existence of the field first.
Cast by C<removeField()>

=item Error: class $package does not implement method $method.

Fatal error: the specific C<$package> (or one of its superclasses) does not
implement this method where it should. This message means that some other
related classes do implement this method however the class at hand does
not.  Probably you should investigate this and probably inform the author
of the package.
Cast by C<notImplemented()>

=item Warning: field objects have an implied name ($name)

Cast by C<build()>

=back

=head1 SEE ALSO

This module is part of Mail-Message version 4.03,
built on January 26, 2026. Website: F<http://perl.overmeer.net/CPAN/>

=head1 LICENSE

For contributors see file ChangeLog.

This software is copyright (c) 2001-2026 by Mark Overmeer.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

