Version 4 introduces a number of massive changes. Probably the most significant change to end-users is the fact that Swift Mailer Version 4 does not work with PHP 4 at all. I have no plans to support PHP 4 so please do not email me and beg me to do so ;)

Besides the system requirements, the interface of Swift has changed significantly in some areas. To the “average” Swift user these changes will no doubt appear as nothing more than a few naming changes, but to those developers who had hacked the previous version of Swift to do add some custom behaviour the changes will jump out immediately. Version 4 has been completely rewritten from the ground up. That is to say, not a single line of code has been taken from Version 3. It’s taken me a long time to finish writing the library because of this fact, but the end result is something I’m extremely proud of. It’s fresh, it’s flexible, it’s test-friendly and I’d like to think that it’s a great demonstration of just what PHP is capable of!

This version of Swift Mailer uses dependency injection everywhere below the surface. For the most part this will be transparent to end-users since I have decorated the constructors where this injection occurs. The dependency injection is one of the primary reasons the library is very test-friendly however.

If you ever tried doing much with international character sets in version 3 there’s a good chance you ran into a few hurdles. Everywhere text processing happens in version 4, the charset is used to ensure text does not become garbled. E-mail requires everything gets sent in 7-bit ascii and then transformed back into it’s 8-bit form at the recipient’s end. Swift Mailer Version 4 includes a completely custom quoted-printable encoder following the rules specified in RFC 2045 to the word. Believe me, meeting all requirements of that RFC is not easy ;)

What! You say? Well, I do have to wonder why I called the various mailing mechanisms in Version 3 “Connections”. Version 3 only spoke in SMTP, so to get Swift Mailer to send an email using the mail() function I had to write a class which conjured up a “fake” SMTP conversation just to make it work. Version 4 takes the abstraction further and replaces all “Connection” classes with “Transport” classes. Each Transport knows whatever language it needs to know; the main Mailer class itself only knows how to use a Transport. What does this mean for you guys? It means faster, more efficient sending, more accurate error messages AND FINALLY! “sendmail -t” support!

Rather than trying to explain this in writing, let me show you two comparisons sending an email with two attachments in version 3, then again in version 4.

$swift = new Swift(new Swift_Connection_SMTP('localhost'));
 
$message = new Swift_Message('My subject');
$message->attach(new Swift_Mime_Part('Reports as requested man!'));
$message->attach(new Swift_Message_Attachment(new Swift_File('report-jan-mar-08.pdf'), 'report-jan-mar-08.pdf', 'application/pdf'));
$message->attach(new Swift_Message_Attachment(new Swift_File('report-mar-jun-08.pdf'), 'report-mar-jun-08.pdf', 'application/pdf'));
 
if ($swift->send($message, new Swift_Address('receiver@domain.tld', 'Person'), new Swift_Address('you@domain.tld', 'You')))
{
  echo "Message sent";
}
else
{
  echo "A problem occurred";
}

$mailer = new Swift_Mailer(new Swift_SmtpTransport('localhost'));
 
$message = Swift_Message::newInstance('My subject', 'Reports as requested man!')
  ->setFrom(array('you@domain.tld' => 'You'))
  ->setTo(array('receiver@domain.tld' => 'Person'))
  ->attach(Swift_Attachment::fromPath('report-jan-mar-08.pdf'))
  ->attach(Swift_Attachment::fromPath('report-mar-jun-08.pdf'));
 
if ($mailer->send($message))
{
  echo "Message sent";
}
else
{
  echo "A problem occurred";
}

Version 4 comes with a new event-driven plugin API. It’s not vastly different from that in Version 3, but it does allow you to cancel events and is in theory faster; though I have not yet benchmarked it.