--- name: "Mail::Message::Construct::Build" section: "3pm" platform: "linux" package: "perl-mail-message" version: "4.05-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/Mail::Message::Construct::Build" --- # Mail::Message::Construct::Build(3pm) building a Mail::Message from components ## NAME Mail::Message::Construct::Build - building a Mail::Message from components ## SYNOPSIS ``` my $msg1 = Mail::Message->build( From => 'me', data => "only two\nlines\n", ); my $msg2 = Mail::Message->buildFromBody($body); Mail::Message->build( From => 'me@myhost.com', To => 'you@yourhost.com', Subject => "Read our folder!", data => \@lines, file => 'folder.pdf', )->send(via => 'postfix'); ``` ## DESCRIPTION Complex functionality on Mail::Message objects is implemented in different files which are autoloaded. This file implements the building of messages from various simpler components. ## METHODS ### Constructing a message - $class-\>**build**( \[$message\|$part\|$body\], @fields, %options ) Simplified message object builder. In case a `$message` or message `$part` is specified, a new message is created with the same body to start with, but new headers. A `$body` may be specified as well. However, there are more ways to add data simply. You may pass `@fields` as objects, even mixed with option PAIRS. The fields will be transmitted in the order they were created, so that might be needed. In the `%options` LIST of paris, all keys which start with a capital are used as header-lines. Lower-cased fields are used for other purposes as listed below. Each field may be used more than once. Pairs where the value is `"undef"` are ignored. If more than one `"data"`, `"file"`, and `"attach"` is specified, a multi-parted message is created. Some `"Content-*"` fields are treated separately: to enforce the content lines of the produced message body **after** it has been created. For instance, to explicitly state that you wish a `"multipart/alternative"` in stead of the default `"multipart/mixed"`. If you wish to specify the type per datum, you need to start playing with Mail::Message::Body objects yourself. This `"build"` method will use **buildFromBody()** when the body object has been constructed. Together, they produce your message. ``` -Option--Default attach undef data undef file undef files [ ] head undef ``` - attach =\> $body\|$part\|$message\|\\@attach One attachment to the message. Each attachment can be full `$message`, a `$part`, or a `$body`. Any `$message` will get encapsulated into a `"message/rfc822"` body. You can specify many items (may be of different types) at once. ``` attach => $folder->message(3)->decoded # body attach => $folder->message(3) # message attach => [ $msg1, $msg2->part(6), $msg3->body ]; ``` - data =\> $text\|\\@lines The `$text` for one part, specified as one string, or an ARRAY of `@lines`. Each line, including the last, must be terminated by a newline. This argument is passed to Mail::Message::Body::new(data) to construct one. ``` data => [ "line 1\n", "line 2\n" ] # array of lines data => <<'TEXT' # string line 1 line 2 TEXT ``` - file =\> $file\|$fh\|$io\|\\@files Create a body where the data is read from the specified `$file` by name, filehandle `$fh`, or `$io` object of type IO::Handle. Also this body is used to create a Mail::Message::Body. \[2.119\] You may even pass more than one file at once: 'file' and 'files' option are equivalent. ``` my $in = IO::File->new('/etc/passwd', 'r'); file => 'picture.jpg' # filename file => $fh # IO::File or GLOB files => [ 'picture.jpg', $fh ] ``` - files =\> \\@files Alias for option `"file"`. - head =\> $head Start with a prepared header, otherwise one is created. » example: ``` my $msg = Mail::Message->build( From => 'me@home.nl', To => Mail::Address->new('your name', 'you@yourplace.aq'), Cc => 'everyone@example.com', Subject => "Let's talk",, $other_message->get('Bcc'), data => [ "This is\n", "the first part of\n", "the message\n" ], file => 'myself.gif', file => 'you.jpg', attach => $signature, ); my $msg = Mail::Message->build( To => 'you', 'Content-Type' => 'text/html', data => "", ); ``` - $class-\>**buildFromBody**($body, \[$head\], $headers) Shape a message around a `$body`. Bodies have information about their content in them, which is used to construct a header for the message. You may specify a `$head` object which is pre-initialized, or one is created for you (also when `$head` is `"undef"`). Next to that, more `$headers` can be specified which are stored in that header. Header fields are added in order, and before the header lines as defined by the body are taken. They may be supplied as key-value pairs or Mail::Message::Field objects. In case of a key-value pair, the field's name is to be used as key and the value is a string, address (Mail::Address object), or array of addresses. A `"Date"`, `"Message-Id"`, and `"MIME-Version"` field are added unless supplied. » example: ``` my $type = Mail::Message::Field->new('Content-Type', 'text/html', 'charset="us-ascii"'); my @to = ( Mail::Address->new('Your name', 'you@example.com'), 'world@example.info', ); my $msg = Mail::Message->buildFromBody($body, From => 'me@example.nl', To => \@to, $type, ); ``` ## DETAILS ### Building a message *Rapid building* Most messages you need to construct are relatively simple. MailBox tries to keep the message content immutable: only the administration around the message may change. Therefore: the only way to create a message is by specifying all content and header fields in one method call. *Compared to* ***MIME::Entity::build()*** The `"build"` method in MailBox is modelled after the `"build"` method as provided by MIMETools, but with a few simplifications: - • When a keys starts with a capital, than it is always a header field - • When a keys is lower-cased, it is always something else - • You use the real field-names, not abbreviations - • All field names are accepted - • You may specify field objects between key-value pairs - • A lot of facts are auto-detected, like content-type and encoding - • You can create a multipart at once Hum, reading the list above... what is equivalent? MIME::Entity is not that simple after all! Let's look at an example from MIME::Entity's manual page: ``` ### Create the top-level, and set up the mail headers: $top = MIME::Entity->build( Type => "multipart/mixed", From => 'me@myhost.com', To => 'you@yourhost.com', Subject => "Hello, nurse!", ); ### Attachment #1: a simple text document: $top->attach(Path=>"./testin/short.txt"); ### Attachment #2: a GIF file: $top->attach( Path => "./docs/mime-sm.gif", Type => "image/gif", Encoding => "base64", ); ### Attachment #3: text we'll create with text we have on-hand: $top->attach(Data => $contents); ``` The MailBox equivalent could be ``` my $msg = Mail::Message->build( From => 'me@myhost.com', To => 'you@yourhost.com', Subject => "Hello, nurse!", file => "./testin/short.txt", file => "./docs/mime-sm.gif", data => $contents, ); ``` One of the simplifications is that MIME::Types is used to lookup the right content type and optimal transfer encoding based on MIME::Types knowledge. Suitable values for Content-Disposition and such fields are added as well. *build, starting with nothing* See **build()**. *buildFromBody, body becomes message* See **buildFromBody()**. *The Content-\* fields* The various `"Content-*"` fields are not as harmless as they look. For instance, the "Content-Type" field will have an effect on the default transfer encoding. When a message is built this way: ``` my $msg = Mail::Message->build( 'Content-Type' => 'video/mpeg3', 'Content-Transfer-Encoding' => 'base64', 'Content-Disposition' => 'attachment', file => '/etc/passwd', ); ``` then first a `"text/plain"` body is constructed (MIME::Types does not find an extension on the filename so defaults to `"text/plain"`), with no encoding. Only when that body is ready, the new type and requested encodings are set. The content of the body will get base64 encoded, because it is requested that way. What basically happens is this: ``` my $head = ...other header lines...; my $body = Mail::Message::Body::Lines->new(file => '/etc/passwd'); $body->type('video/mpeg3'); $body->transferEncoding('base64'); $body->disposition('attachment'); my $msg = Mail::Message->buildFromBody($body, $head); ``` A safer way to construct the message is: ``` my $body = Mail::Message::Body::Lines->new( file => '/etc/passwd', mime_type => 'video/mpeg3', transfer_encoding => 'base64', disposition => 'attachment', ); my $msg = Mail::Message->buildFromBody( $body, ...other header lines... ); ``` In the latter program, you will immediately start with a body of the right type. ## DIAGNOSTICS - Error: only **build()** Mail::Message's; they are not in a folder yet. You may wish to construct a message to be stored in a some kind of folder, but you need to do that in two steps. First, create a normal Mail::Message, and then add it to the folder. During this **Mail::Box::addMessage()** process, the message will get **coerce()**-d into the right message type, adding storage information and the like. Cast by `build()` - Warning: skipped unknown key '$key' in build. Cast by `build()` ## 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.