Mail::Message::Head(3)

NAME
Mail::Message::Head - the header of one message

INHERITANCE
 Mail::Message::Head
   is a Mail::Reporter

 Mail::Message::Head is extended by
   Mail::Box::IMAP4::Head
   Mail::Message::Head::Complete
   Mail::Message::Head::Delayed
   Mail::Message::Head::Subset

SYNOPSIS
  my $head = Mail::Message::Head->new;
  $head->add('From: me@localhost');
  $head->add(From => 'me@localhost');
  $head->add(Mail::Message::Field->new(From => 'me'));
  my $subject = $head->get('subject');
  my @rec = $head->get('received');
  $head->delete('From');

DESCRIPTION
"Mail::Message::Head" MIME headers are part of Mail::Message messages, which are grouped in Mail::Box folders.

A long list of standard MIME header fields with definitions can be found in RFC4021 (<https://www.rfc-editor.org/rfc/rfc4021.html>) and its updates RFC5322 and RFC6854.

ATTENTION!!! most functionality about e-mail headers is described in Mail::Message::Head::Complete, which is a matured header object. Other kinds of headers will be translated to that type when time comes.

On this page, the general methods which are available on any header are described. Read about differences in the sub-class specific pages.

Extends "DESCRIPTION" in Mail::Reporter.

OVERLOADED

overload: "" stringifaction
    The header, when used as string, will format as if Mail::Message::Head::Complete::string() was called, so return a nicely folder full header. An exception is made for Carp, which will get a simplified string to avoid unreadible messages from "croak" and "confess".

    » example: using a header object as string

      print $head;     # implicit stringification by print
      $head->print;    # the same

      print "$head";   # explicit stringication

overload: bool true/false
    When the header does not contain any lines (which is illegal, according to the RFCs), "false" is returned. In all other cases, a "true" value is produced.

METHODS
Extends "METHODS" in Mail::Reporter.

  Constructors
Extends "Constructors" in Mail::Reporter.

$class->build( [PAIR|$field]-LIST )
    A fast way to construct a header with many lines. The PAIRs are "(name, content)" pairs of the header, but it is also possible to pass Mail::Message::Field objects. A Mail::Message::Head::Complete header is created by simply calling Mail::Message::Head::Complete::build(), and then each field is added. Double field names are permitted.

    » example:

      my $subject = Mail::Message::Field->new(Subject => 'xyz');

      my $head = Mail::Message::Head->build(
        From     => 'me@example.com',
        To       => 'you@anywhere.aq',
        $subject,
        Received => 'one',
        Received => 'two',
      );

      print ref $head;
       # -->  Mail::Message::Head::Complete

$class->new(%options)
    Create a new message header object. The object will store all the fields of a header. When you get information from the header, it will be returned to you as Mail::Message::Field objects, although the fields may be stored differently internally.

    If you try to instantiate a Mail::Message::Head, you will automatically be upgraded to a Mail::Message::Head::Complete --a full head. Improves base, see "Constructors" in Mail::Reporter

     -Option    --Default
      field_type  Mail::Message::Field::Fast
      message     undef
      modified    false

    field_type => CLASS
        The type of objects that all the fields will have. This must be an extension of Mail::Message::Field.

    message => $message
        The $message where this header belongs to. Usually, this is not known at creation of the header, but sometimes it is. If not, call the message() method later to set it.

    modified => BOOLEAN

  Attributes
Extends "Attributes" in Mail::Reporter.

  The header

$obj->isDelayed()
    Headers may only be partially read, in which case they are called delayed. This method returns "true" if some header information still needs to be read. Returns "false" if all header data has been read. Will never trigger completion.

$obj->isEmpty()
    Are there any fields defined in the current header? Be warned that the header will not be loaded for this: delayed headers will return "true" in any case.

$obj->isModified()
    Returns whether the header has been modified after being read.

    » example:

      if($head->isModified) { ... }

$obj->knownNames()
    Like Mail::Message::Head::Complete::names(), but only returns the known header fields, which may be less than "names" for header types which are partial. names() will trigger completion, where knownNames() does not.

$obj->message( [$message] )
    Get (after setting) the message where this header belongs to. This does not trigger completion.

$obj->modified( [BOOLEAN] )
    Sets the modified flag to "BOOLEAN". Without value, the current setting is returned, but in that case you can better use isModified(). Changing this flag will not trigger header completion.

    » example:

      $head->modified(1);
      if($head->modified) { ... }
      if($head->isModified) { ... }

$obj->orderedFields()
    Returns the fields ordered the way they were read or added.

  Access to the header

$obj->get( $name, [$index] )
    Get the data which is related to the field with the $name. The case of the characters in $name does not matter.

    If there is only one data element defined for the $name, or if there is an $index specified as the second argument, only the specified element will be returned. If the field $name matches more than one header the return value depends on the context. In LIST context, all values will be returned in the order they are read. In SCALAR context, only the last value will be returned.

    » example:

      my $head = Mail::Message::Head->new;
      $head->add('Received: abc');
      $head->add('Received: xyz');
      $head->add('Subject: greetings');

      my @rec_list   = $head->get('Received');
      my $rec_scalar = $head->get('Received');
      print ",@rec_list,$rec_scalar,"     # ,abc xyz, xyz,
      print $head->get('Received', 0);    # abc
      my @sub_list   = $head->get('Subject');
      my $sub_scalar = $head->get('Subject');
      print ",@sub_list,$sub_scalar,"     # ,greetings, greetings,

$obj->study( $name, [$index] )
    Like get(), but puts more effort in understanding the contents of the field. Mail::Message::Field::study() will be called for the field with the specified FIELDNAME, which returns Mail::Message::Field::Full objects. In scalar context only the last field with that name is returned. When an $index is specified, that element is returned.

  About the body

$obj->guessBodySize()
    Try to estimate the size of the body of this message, but without parsing the header or body. The result might be "undef" or a few percent of the real size. It may even be very far of the real value, that's why this is a guess.

$obj->isMultipart()
    Returns whether the body of the related message is a multipart body. May trigger completion, when the "Content-Type" field is not defined.

  Internals

$obj->addNoRealize($field)
    Add a field, like Mail::Message::Head::Complete::add() does, but avoid the loading of a possibly partial header. This method does not test the validity of the argument, nor flag the header as changed. This does not trigger completion.

$obj->addOrderedFields($fields)

$obj->fileLocation()
    Returns the location of the header in the file, as a pair begin and end. The begin is the first byte of the header. The end is the first byte after the header.

$obj->load()
    Be sure that the header is loaded. This returns the loaded header object.

$obj->moveLocation($distance)
    Move the registration of the header in the file.

$obj->read($parser)
    Read the header information of one message into this header structure. This method is called by the folder object (some Mail::Box sub-class), which passes the $parser as an argument.

$obj->setNoRealize($field)
    Set a field, but avoid the loading of a possibly partial header as set() does. This method does not test the validity of the argument, nor flag the header as changed. This does not trigger completion.

  Error handling
Extends "Error handling" in Mail::Reporter.

$obj->AUTOLOAD()
    Inherited, see "Error handling" in Mail::Reporter

$obj->notImplemented()
    Inherited, see "Error handling" in Mail::Reporter

  Cleanup
Extends "Cleanup" in Mail::Reporter.

$obj->DESTROY()
    Inherited, see "Cleanup" in Mail::Reporter

DETAILS

  Ordered header fields
Many Perl implementations make a big mistake by disturbing the order of header fields. For some fields (especially the resent groups, see Mail::Message::Head::ResentGroup) the order shall be maintained.

MailBox will keep the order of the fields as they were found in the source. When your add a new field, it will be added at the end. If your replace a field with a new value, it will stay in the original order.

  Head class implementation
The header of a MIME message object contains a set of lines, which are called fields (by default represented by Mail::Message::Field objects). Dependent on the situation, the knowledge about the fields can be in one of three situations, each represented by a sub-class of this module:

•   Mail::Message::Head::Complete

    In this case, it is sure that all knowledge about the header is available. When you get() information from the header and it is not there, it will never be there.

•   Mail::Message::Head::Subset

    There is no certainty whether all header lines are known (probably not). This may be caused as result of reading a fast index file, as described in Mail::Box::MH::Index. The object is automatically transformed into a Mail::Message::Head::Complete when all header lines must be known.

•   Mail::Message::Head::Partial

    A partial header is like a subset header: probably the header is incomplete. The means that you are not sure whether a get() for a field fails because the field is not a part of the message or that it fails because it is not yet known to the program. Where the subset header knows where to get the other fields, the partial header does not know it. It cannot hide its imperfection.

•   Mail::Message::Head::Delayed

    In this case, there is no single field known. Access to this header will always trigger the loading of the full header.

  Subsets of header fields
Message headers can be quite large, and therefore MailBox provides simplified access to some subsets of information. You can grab these sets of fields together, create and delete them as group.

On the moment, the following sets are defined:

•   Mail::Message::Head::ResentGroup

    A resent group is a set of fields which is used to log one step in the transmission of the message from the original sender to the destination.

    Each step adds a set of headers to indicate when the message was received and how it was forwarded (without modification). These fields are best created using Mail::Message::bounce().

•   Mail::Message::Head::ListGroup

    Fields which are used to administer and log mailing list activity. Mailing list software has to play trics with the original message to be able to get the reply on that message back to the mailing list. Usually a large number of lines are added.

•   Mail::Message::Head::SpamGroup

    A set of fields which contains header fields which are produced by spam detection software. You may want to remove these fields when you store a message for a longer period of time.

DIAGNOSTICS

Error: class $package does not implement method $method.
    Fatal error: the specific $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 notImplemented()

SEE ALSO
This module is part of Mail-Message version 4.05, built on April 10, 2026. Website: http://perl.overmeer.net/mailbox/

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.