Sending Messages

The SMTP Transport

The SMTP Transport sends messages over the (standardized) Simple Message Transfer Protocol. It can deal with encryption and authentication.

The SMTP Transport, Swift_SmtpTransport is without doubt the most commonly used Transport because it will work on 99% of web servers (I just made that number up, but you get the idea). All the server needs is the ability to connect to a remote (or even local) SMTP server on the correct port number (usually 25).

SMTP servers often require users to authenticate with a username and password before any mail can be sent to other domains. This is easily achieved using Swift Mailer with the SMTP Transport.

SMTP is a protocol -- in other words it's a "way" of communicating a job to be done (i.e. sending a message). The SMTP protocol is the fundamental basis on which messages are delivered all over the internet 7 days a week, 365 days a year. For this reason it's the most "direct" method of sending messages you can use and it's the one that will give you the most power and feedback (such as delivery failures) when using Swift Mailer.

Because SMTP is generally run as a remote service (i.e. you connect to it over the network/internet) it's extremely portable from server-to-server. You can easily store the SMTP server address and port number in a configuration file within your application and adjust the settings accordingly if the code is moved or if the SMTP server is changed.

Some SMTP servers -- Google for example -- use encryption for security reasons. Swift Mailer supports using both ssl (SMTPS = SMTP over TLS) and tls (SMTP with STARTTLS) encryption settings.

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// Create the Transport
$transport = new Swift_SmtpTransport('smtp.example.org', 25);

// Create the Mailer using your created Transport
$mailer = new Swift_Mailer($transport);

/*
It's also possible to use multiple method calls

$transport = (new Swift_SmtpTransport())
  ->setHost('smtp.example.org')
  ->setPort(25)
  ;
*/

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// Create the Transport
// Option #1: SMTPS = SMTP over TLS (always encrypted):
$transport = new Swift_SmtpTransport('smtp.example.org', 587, 'ssl');
// Option #2: SMTP with STARTTLS (best effort encryption):
$transport = new Swift_SmtpTransport('smtp.example.org', 587, 'tls');

// Create the Mailer using your created Transport
$mailer = new Swift_Mailer($transport);

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// Create the Transport the call setUsername() and setPassword()
$transport = (new Swift_SmtpTransport('smtp.example.org', 25))
  ->setUsername('username')
  ->setPassword('password')
  ;

// Create the Mailer using your created Transport
$mailer = new Swift_Mailer($transport);

The Sendmail Transport

The Sendmail Transport sends messages by communicating with a locally installed MTA -- such as sendmail.

The Sendmail Transport, Swift_SendmailTransport does not directly connect to any remote services. It is designed for Linux servers that have sendmail installed. The Transport starts a local sendmail process and sends messages to it. Usually the sendmail process will respond quickly as it spools your messages to disk before sending them.

The Transport is named the Sendmail Transport for historical reasons (sendmail was the "standard" UNIX tool for sending e-mail for years). It will send messages using other transfer agents such as Exim or Postfix despite its name, provided they have the relevant sendmail wrappers so that they can be started with the correct command-line flags.

It's a common misconception that because the Sendmail Transport returns a result very quickly it must therefore deliver messages to recipients quickly -- this is not true. It's not slow by any means, but it's certainly not faster than SMTP when it comes to getting messages to the intended recipients. This is because sendmail itself sends the messages over SMTP once they have been quickly spooled to disk.

The Sendmail Transport has the potential to be just as smart of the SMTP Transport when it comes to notifying Swift Mailer about which recipients were rejected, but in reality the majority of locally installed sendmail instances are not configured well enough to provide any useful feedback. As such Swift Mailer may report successful deliveries where they did in fact fail before they even left your server.

You can run the Sendmail Transport in two different modes specified by command line flags:

• "-bs" runs in SMTP mode so theoretically it will act like the SMTP Transport
• "-t" runs in piped mode with no feedback, but theoretically faster, though not advised

You can think of the Sendmail Transport as a sort of asynchronous SMTP Transport -- though if you have problems with delivery failures you should try using the SMTP Transport instead. Swift Mailer isn't doing the work here, it's simply passing the work to somebody else (i.e. sendmail).

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// Create the Transport
$transport = new Swift_SendmailTransport('/usr/sbin/exim -bs');

// Create the Mailer using your created Transport
$mailer = new Swift_Mailer($transport);

Using the send() Method

The send() method of the Swift_Mailer class sends a message using exactly the same logic as your Desktop mail client would use. Just pass it a Message and get a result.

The message will be sent just like it would be sent if you used your mail client. An integer is returned which includes the number of successful recipients. If none of the recipients could be sent to then zero will be returned, which equates to a boolean false. If you set two To: recipients and three Bcc: recipients in the message and all of the recipients are delivered to successfully then the value 5 will be returned:

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// Create the Transport
$transport = new Swift_SmtpTransport('localhost', 25);

// Create the Mailer using your created Transport
$mailer = new Swift_Mailer($transport);

// Create a message
$message = (new Swift_Message('Wonderful Subject'))
  ->setFrom(['john@doe.com' => 'John Doe'])
  ->setTo(['receiver@domain.org', 'other@domain.org' => 'A name'])
  ->setBody('Here is the message itself')
  ;

// Send the message
$numSent = $mailer->send($message);

printf("Sent %d messages\n", $numSent);

/* Note that often that only the boolean equivalent of the
   return value is of concern (zero indicates FALSE)

if ($mailer->send($message))
{
  echo "Sent\n";
}
else
{
  echo "Failed\n";
}

*/

Sending Emails in Batch

If you want to send a separate message to each recipient so that only their own address shows up in the To: field, follow the following recipe:

• Create a Transport from one of the provided Transports -- Swift_SmtpTransport, Swift_SendmailTransport, or one of the aggregate Transports.
• Create an instance of the Swift_Mailer class, using the Transport as it's constructor parameter.
• Create a Message.
• Iterate over the recipients and send message via the send() method on the Mailer object.

Each recipient of the messages receives a different copy with only their own email address on the To: field.

Make sure to add only valid email addresses as recipients. If you try to add an invalid email address with setTo(), setCc() or setBcc(), Swift Mailer will throw a Swift_RfcComplianceException.

If you add recipients automatically based on a data source that may contain invalid email addresses, you can prevent possible exceptions by validating the addresses using Egulias\EmailValidator\EmailValidator (a dependency that is installed with Swift Mailer) and only adding addresses that validate. Another way would be to wrap your setTo(), setCc() and setBcc() calls in a try-catch block and handle the Swift_RfcComplianceException in the catch block.

Handling invalid addresses properly is especially important when sending emails in large batches since a single invalid address might cause an unhandled exception and stop the execution or your script early.

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// Create the Transport
$transport = new Swift_SmtpTransport('localhost', 25);

// Create the Mailer using your created Transport
$mailer = new Swift_Mailer($transport);

// Create a message
$message = (new Swift_Message('Wonderful Subject'))
  ->setFrom(['john@doe.com' => 'John Doe'])
  ->setBody('Here is the message itself')
  ;

// Send the message
$failedRecipients = [];
$numSent = 0;
$to = ['receiver@domain.org', 'other@domain.org' => 'A name'];

foreach ($to as $address => $name)
{
  if (is_int($address)) {
    $message->setTo($name);
  } else {
    $message->setTo([$address => $name]);
  }

  $numSent += $mailer->send($message, $failedRecipients);
}

printf("Sent %d messages\n", $numSent);

Getting Failures By-reference

Collecting delivery failures by-reference with the send() method is as simple as passing a variable name to the method call:

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$mailer = new Swift_Mailer( ... );

$message = (new Swift_Message( ... ))
  ->setFrom( ... )
  ->setTo([
    'receiver@bad-domain.org' => 'Receiver Name',
    'other@domain.org' => 'A name',
    'other-receiver@bad-domain.org' => 'Other Name'
  ))
  ->setBody( ... )
  ;

// Pass a variable name to the send() method
if (!$mailer->send($message, $failures))
{
  echo "Failures:";
  print_r($failures);
}

/*
Failures:
Array (
  0 => receiver@bad-domain.org,
  1 => other-receiver@bad-domain.org
)
*/

If the Transport rejects any of the recipients, the culprit addresses will be added to the array provided by-reference.