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18.3. Sending Mail

18.3.1. Problem

You
want your program to send mail. Some programs monitor system
resources like disk space and notify appropriate people when disk
space becomes dangerously low. CGI script authors may not want
programs to report errors like "the database is down" to the user,
preferring instead to send mail to the database administrator about
the problem.

18.3.2. Solution

Use the CPAN module Mail::Mailer:

use Mail::Mailer;
$mailer = Mail::Mailer->new("sendmail");
$mailer->open({ From    => $from_address,
To      => $to_address,
Subject => $subject,
})
or die "Can't open: $!\n";
print $mailer $body;
$mailer->close( );

Or use the sendmail program
directly:

open(SENDMAIL, "|/usr/lib/sendmail -oi -t -odq")
or die "Can't fork for sendmail: $!\n";
print SENDMAIL <<"EOF";
From: User Originating Mail <me\@host>
To: Final Destination <you\@otherhost>
Subject: A relevant subject line
Body of the message goes here, in as many lines as you like.
EOF
close(SENDMAIL)or warn "sendmail didn't close nicely";

18.3.3. Discussion

You have three choices for
sending mail from your program. You can call another program normally
used to send mail, such as Mail or
mailx; these are called MUAs or Mail
User Agents. You can use a system-level mail program, such
as sendmail; this is an MTA, or Mail
Transport Agent. Or you can connect to an Simple Mail
Transfer Protocol (SMTP) server. Unfortunately, there's no standard
user-level mail program, sendmail doesn't have a
standard location, and SMTP isn't particularly simple. The CPAN
module Mail::Mailer hides these complexities from you.

Create a Mail::Mailer object with
Mail::Mailer->new. If you don't pass any
arguments, it uses the default mail sending method (probably a
program like mail). Arguments to
new select an alternate way to send the message.
The first argument is the type of delivery method
("mail" for a Unix mail user agent,
"sendmail" for sendmail, and
"smtp" to connect to an SMTP server). The optional
second argument is that program's path.

For instance, to instruct Mail::Mailer to use
sendmail instead of its default:

$mailer = Mail::Mailer->new("sendmail");

Here's how to tell it to use
/u/gnat/bin/funkymailer instead of
mail:

$mailer = Mail::Mailer->new("mail", "/u/gnat/bin/funkymailer");

Here's how to use SMTP with the machine
mail.myisp.com as the mail server:

$mailer = Mail::Mailer->new("smtp", "mail.myisp.com");

If an error occurs at any part of Mail::Mailer,
die is called. To check for these exceptions, wrap
your mail-sending code in eval and check
$@ afterward:

eval {
$mailer = Mail::Mailer->new("bogus", "arguments");
# ...
};
if ($@) {
# the eval failed
print "Couldn't send mail: $@\n";
} else {
# the eval succeeded
print "The authorities have been notified.\n";
}

The new constructor raises an exception if you
provide arguments it doesn't understand, or if you specify no
arguments and it doesn't have a default method. Mail::Mailer won't
run a program or connect to the SMTP server until you call the
open method with the message headers:

$mailer->open( { From    => 'Nathan Torkington <gnat@frii.com>',
To      => 'Tom Christiansen <tchrist@perl.com>',
Subject => 'The Perl Cookbook' } );

The open method raises an exception if the program
or server couldn't be opened. If open succeeds,
you may treat $mailer as a filehandle and print
the body of your message to it:

print $mailer << EO_SIG;
Are we ever going to finish this book?
My wife is threatening to leave me.
She says I love EMACS more than I love her.
Do you have a recipe that can help me?
Nat
EO_SIG

When you're done, call the close function on the
Mail::Mailer object:

close($mailer) or die "can't close mailer: $!";

If you want to go it alone and communicate with
sendmail directly, use something like this:

open(SENDMAIL, "|/usr/sbin/sendmail -oi -t -odq")
or die "Can't fork for sendmail: $!\n";
print SENDMAIL << "EOF";
From: Fancy Chef <chef@example.com>
To: Grubby Kitchenhand <hand@example.com>
Subject: Re: The Perl Cookbook
(1) We will never finish the book.
(2) No man who uses EMACS is deserving of love.
(3) I recommend coq au vi.
Frank Wah
EOF
close(SENDMAIL);

This is a straightforward use of open to run
another program (see Recipe 16.4). You need
to specify the full path to sendmail because its
location varies from machine to machine. It is often found in places
like /usr/lib or /usr/sbin.
The flags we give to sendmail say not to exit
when a line with only a dot is read (-oi), to read
the message headers to decide whom to send it to
(-t), and to queue the message instead of
attempting immediate delivery (-odq). This last
option is important only when sending many messages (in bulk);
omitting it would quickly swamp the machine with
sendmail processes. For immediate delivery of
your message (for instance, you're testing your program or the mail
is urgent), remove -odq from the command line.

We print an entire message, headers and then body,
separated by a blank line. There are no special escapes to insert
newlines (as some user mail programs have), so all text is literal.
sendmail adds headers like
Date and Message-ID, which you
shouldn't generate yourself anyway.

Some ports of Perl (Windows and Mac OS 9 particularly) don't have
sendmail or mail. In these
cases, you should find yourself a receptive SMTP server.

18.3.4. See Also

The open function in Chapter 29 of
Programming Perl and in
perlfunc(1); Recipe 16.4; Recipe 16.10; Recipe 16.19; Recipe 19.5;
the RFCs dictating the SMTP protocol, RFC 821, Simple Mail
Transfer Protocol, as amended by later RFCs; the
documentation for the Mail::Mailer module from CPAN