Provided by: libmail-message-perl_3.019-1_all 
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 --Defined in --Default
field_type Mail::Message::Field::Fast
log Mail::Reporter 'WARNINGS'
message undef
modified false
trace Mail::Reporter 'WARNINGS'
field_type => CLASS
The type of objects that all the fields will have. This must be an extension of
Mail::Message::Field.
log => LEVEL
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
trace => LEVEL
Attributes
Extends "Attributes" in Mail::Reporter.
$obj->logSettings()
Inherited, see "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
$obj->addReport($object)
Inherited, see "Error handling" in Mail::Reporter
$any->defaultTrace( [$level]|[$loglevel, $tracelevel]|[$level, $callback] )
Inherited, see "Error handling" in Mail::Reporter
$obj->errors()
Inherited, see "Error handling" in Mail::Reporter
$any->log( [$level, [$strings]] )
Inherited, see "Error handling" in Mail::Reporter
$any->logPriority($level)
Inherited, see "Error handling" in Mail::Reporter
$obj->notImplemented()
Inherited, see "Error handling" in Mail::Reporter
$obj->report( [$level] )
Inherited, see "Error handling" in Mail::Reporter
$obj->reportAll( [$level] )
Inherited, see "Error handling" in Mail::Reporter
$obj->trace( [$level] )
Inherited, see "Error handling" in Mail::Reporter
$obj->warnings()
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: Package $package does not implement $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 3.019, built on November 24, 2025. Website:
http://perl.overmeer.net/CPAN/
LICENSE
For contributors see file ChangeLog.
This software is copyright (c) 2001-2025 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.
perl v5.40.1 2025-12-07 Mail::Message::Head(3pm)