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Module Version: 2.106   Source   Latest Release: Mail-Box-3.003


Mail::Box::MH - handle MH folders


   is a Mail::Box::Dir
   is a Mail::Box
   is a Mail::Reporter


 use Mail::Box::MH;
 my $folder = new Mail::Box::MH folder => $ENV{MAIL}, ...;


This documentation describes how MH mailboxes work, and what you can do with the MH folder object Mail::Box::MH.


overload: ""()

See "OVERLOADED" in Mail::Box

overload: @{}()

See "OVERLOADED" in Mail::Box

overload: cmp()

See "OVERLOADED" in Mail::Box



 -Option           --Defined in     --Default
  access             Mail::Box        'r'
  body_delayed_type  Mail::Box        Mail::Message::Body::Delayed
  body_type          Mail::Box        Mail::Message::Body::Lines
  coerce_options     Mail::Box        []
  create             Mail::Box        <false>
  directory          Mail::Box::Dir   <derived from folder name>
  extract            Mail::Box        10240
  field_type         Mail::Box        undef
  fix_headers        Mail::Box        <false>
  folder             Mail::Box        $ENV{MAIL}
  folderdir          Mail::Box        $ENV{HOME}/.mh
  head_delayed_type  Mail::Box        Mail::Message::Head::Delayed
  head_type          Mail::Box        Mail::Message::Head::Complete
  index                               undef
  index_filename                      <foldername>/.index
  index_type                          Mail::Box::MH::Index
  keep_dups          Mail::Box        <false>
  keep_index                          0
  labels                              undef
  labels_filename                     <foldername>/.mh_sequence
  labels_type                         Mail::Box::MH::Labels
  lock_file          Mail::Box        <index_file>
  lock_timeout       Mail::Box        1 hour
  lock_type          Mail::Box        Mail::Box::Locker::DotLock
  lock_wait          Mail::Box        10 seconds
  locker             Mail::Box        undef
  log                Mail::Reporter   'WARNINGS'
  manager            Mail::Box        undef
  message_type       Mail::Box        Mail::Box::Message
  multipart_type     Mail::Box        Mail::Message::Body::Multipart
  remove_when_empty  Mail::Box        <true>
  save_on_exit       Mail::Box        <true>
  trace              Mail::Reporter   'WARNINGS'
  trusted            Mail::Box        <depends on folder location>
access => MODE
body_delayed_type => CLASS
body_type => CLASS|CODE
coerce_options => ARRAY
create => BOOLEAN
directory => DIRECTORY
field_type => CLASS
fix_headers => BOOLEAN
folder => FOLDERNAME
folderdir => DIRECTORY
head_delayed_type => CLASS
head_type => CLASS
index => OBJECT

You may specify an OBJECT of a type which extends Mail::Box::MH::Index (at least implements a get() method), as alternative for an index file reader as created by Mail::Box::MH.

index_filename => FILENAME

The FILENAME which is used in each directory to store the headers of all mails. The filename shall not contain a directory path. (e.g. Do not use /usr/people/jan/.index, nor subdir/.index, but say .index.)

index_type => CLASS
keep_dups => BOOLEAN
keep_index => BOOLEAN

Keep an index file of the specified mailbox, one file per directory. Using an index file will speed up things considerably, because it avoids reading all the message files the moment that you open the folder. When you open a folder, you can use the index file to retrieve information such as the subject of each message, instead of having to read possibly thousands of messages.

labels => OBJECT

You may specify an OBJECT of a type which extends Mail::Box::MH::Labels (at least implements the get() method), as alternative for labels file reader as created by Mail::Box::MH.

labels_filename => FILENAME

In MH-folders, messages can be labeled, for instance based on the sender or whether it is read or not. This status is kept in a file which is usually called .mh_sequences, but that name can be overruled with this flag.

labels_type => CLASS
lock_file => FILENAME
lock_timeout => SECONDS
lock_wait => SECONDS
locker => OBJECT
log => LEVEL
manager => MANAGER
message_type => CLASS
multipart_type => CLASS
remove_when_empty => BOOLEAN
save_on_exit => BOOLEAN
trace => LEVEL
trusted => BOOLEAN

The folder

$obj->addMessage(MESSAGE, OPTIONS)

See "The folder" in Mail::Box

$obj->addMessages(MESSAGE [, MESSAGE, ...])

See "The folder" in Mail::Box


Append a message to a folder which is not open.

 -Option  --Defined in     --Default
  folder    Mail::Box        <required>
  message   Mail::Box        undef
  messages  Mail::Box        undef
  share     Mail::Box        <false>
folder => FOLDERNAME
message => MESSAGE
share => BOOLEAN

See "The folder" in Mail::Box

$obj->copyTo(FOLDER, OPTIONS)

See "The folder" in Mail::Box


See "The folder" in Mail::Box


See "The folder" in Mail::Box::Dir


See "The folder" in Mail::Box


See "The folder" in Mail::Box


See "The folder" in Mail::Box


See "The folder" in Mail::Box


See "The folder" in Mail::Box


See "The folder" in Mail::Box


See "The folder" in Mail::Box

Folder flags


See "Folder flags" in Mail::Box


See "Folder flags" in Mail::Box


See "Folder flags" in Mail::Box


See "Folder flags" in Mail::Box

The messages


See "The messages" in Mail::Box


See "The messages" in Mail::Box

$obj->findFirstLabeled(LABEL, [BOOLEAN, [ARRAY-OF-MSGS]])

See "The messages" in Mail::Box

$obj->message(INDEX [,MESSAGE])

See "The messages" in Mail::Box

$obj->messageId(MESSAGE-ID [,MESSAGE])

See "The messages" in Mail::Box


See "The messages" in Mail::Box


See "The messages" in Mail::Box


See "The messages" in Mail::Box


See "The messages" in Mail::Box



See "Sub-folders" in Mail::Box

$obj->nameOfSubFolder(SUBNAME, [PARENTNAME])
Mail::Box::MH->nameOfSubFolder(SUBNAME, [PARENTNAME])

See "Sub-folders" in Mail::Box


See "Sub-folders" in Mail::Box

$obj->openSubFolder(SUBNAME, OPTIONS)

See "Sub-folders" in Mail::Box


See "Sub-folders" in Mail::Box


$obj->coerce(MESSAGE, OPTIONS)

See "Internals" in Mail::Box

Mail::Box::MH->create(FOLDERNAME, OPTIONS)
 -Option   --Defined in--Default
  folderdir  Mail::Box   undef
folderdir => DIRECTORY
$obj->determineBodyType(MESSAGE, HEAD)

See "Internals" in Mail::Box

$obj->folderToDirectory(FOLDERNAME, FOLDERDIR)

See "Internals" in Mail::Box::Dir

Mail::Box::MH->foundIn([FOLDERNAME], OPTIONS)

See "Internals" in Mail::Box


Returns the highest number which is used in the folder to store a file. This method may be called when the folder is read (then this number can be derived without file-system access), but also when the folder is not read (yet).


Create a index reader/writer object.


Create a label reader/writer object.


See "Internals" in Mail::Box


See "Internals" in Mail::Box


See "Internals" in Mail::Box


See "Internals" in Mail::Box::Dir


See "Internals" in Mail::Box


See "Internals" in Mail::Box


See "Internals" in Mail::Box


See "Internals" in Mail::Box


See "Internals" in Mail::Box


See "Internals" in Mail::Box

 -Option  --Defined in     --Default
  messages  Mail::Box        <required>
  renumber                   <true>
messages => ARRAY
renumber => BOOLEAN

Permit renumbering of message. By default this is true, but for some unknown reason, you may be thinking that messages should not be renumbered.

Other methods


See "Other methods" in Mail::Box

Error handling


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter

$obj->log([LEVEL [,STRINGS]])
Mail::Box::MH->log([LEVEL [,STRINGS]])

See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter


See "Error handling" in Mail::Reporter



See "Cleanup" in Mail::Box


See "Cleanup" in Mail::Reporter


Different kinds of folders

Available folder types

Folder class implementation

How MH folders work

MH-type folders use a directory to store the messages of one folder. Each message is stored in a separate file. This seems useful, because changes in a folder change only a few of these small files, in contrast with file-based folders where changes in a folder cause rewrites of huge folder files.

However, MH-based folders perform very bad if you need header information of all messages. For instance, if you want to have full knowledge about all message-threads (see Mail::Box::Thread::Manager) in the folder, it requires to read all header lines in all message files. And usually, reading your messages in threads is desired.

So, each message is written in a separate file. The filenames are numbers, which count from 1. Next to these message files, a directory may contain a file named .mh_sequences, storing labels which relate to the messages. Furthermore, a folder-directory may contain sub-directories, which are seen as sub-folders.

This implementation

This implementation supports the .mh-sequences file and sub-folders. Next to this, considerable effort it made to avoid reading each message-file. This should boost performance of the MailBox distribution over other Perl-modules which are able to read folders.

Folder types which store their messages each in one file, together in one directory, are bad for performance. Consider that you want to know the subjects of all messages, while browser through a folder with your mail-reading client. This would cause all message-files to be read.

Mail::Box::MH has two ways to try improve performance. You can use an index-file, and use on delay-loading. The combination performs even better. Both are explained in the next sections.

An index-file

If you specify new(keep_index), then all header-lines of all messages from the folder which have been read once, will also be written into one dedicated index-file (one file per folder). The default filename is .index

However, index-files are not supported by any other reader which supports MH (as far as I know). If you read the folders with such I client, it will not cause unrecoverable conflicts with this index-file, but at most be bad for performance.

If you do not (want to) use an index-file, then delay-loading may save your day.


Error: Cannot append message without lock on $folder.

It is impossible to append one or more messages to the folder which is not opened, because locking it failes. The folder may be in use by an other application, or you may need to specify some lock related options (see new()).

Error: Cannot create MH folder $name: $!

For some reason, it is impossible to create the folder. Check the permissions and the name of the folder. Does the path to the directory to be created exist?

Error: Cannot write folder $name without lock.

It is impossible to get a lock on the folder, which means that the changes can not be made. You may need to tune the lock related options which are available at folder creation.

Warning: Changes not written to read-only folder $self.

You have opened the folder read-only --which is the default set by new(access)--, made modifications, and now want to close it. Set close(force) if you want to overrule the access mode, or close the folder with close(write) set to NEVER.

Error: Copying failed for one message.

For some reason, for instance disc full, removed by external process, or read-protection, it is impossible to copy one of the messages. Copying will proceed for the other messages.

Error: Destination folder $name is not writable.

The folder where the messages are copied to is not opened with write access (see new(access)). This has no relation with write permission to the folder which is controled by your operating system.

Warning: Different messages with id $msgid

The message id is discovered more than once within the same folder, but the content of the message seems to be different. This should not be possible: each message must be unique.

Error: Folder $name is opened read-only

You can not write to this folder unless you have opened the folder to write or append with new(access), or the force option is set true.

Error: Folder $name not deleted: not writable.

The folder must be opened with write access via new(access), otherwise removing it will be refused. So, you may have write-access according to the operating system, but that will not automatically mean that this delete method permits you to. The reverse remark is valid as well.

Error: Invalid timespan '$timespan' specified.

The string does not follow the strict rules of the time span syntax which is permitted as parameter.

Warning: Message-id '$msgid' does not contain a domain.

According to the RFCs, message-ids need to contain a unique random part, then an @, and then a domain name. This is made to avoid the creation of two messages with the same id. The warning emerges when the @ is missing from the string.

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.

Error: Unable to create subfolder $name of $folder.

The copy includes the subfolders, but for some reason it was not possible to copy one of these. Copying will proceed for all other sub-folders.

Error: Unable to write message for $folder to $filename: $!

The new message could not be written to its new file, for the specific reason.

Error: Writing folder $name failed

For some reason (you probably got more error messages about this problem) it is impossible to write the folder, although you should because there were changes made.


This module is part of Mail-Box distribution version 2.106, built on August 15, 2012. Website:


Copyrights 2001-2012 by [Mark Overmeer]. For other contributors see ChangeLog.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See

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