What's the differences between the Mailer and the Message classes?

Question

In the Craft 3 Class Reference (https://docs.craftcms.com/api/v3), there are two classes under craft\mail:

• Mailer
• Message

I found that I was able to send an email using this:

<?php 

use craft\mail\Message;

$message = new Message();
$message->setTo('john@doe.com');
$message->setSubject("Hello world.");
$message->setHtmlBody("Hello world.");
$message->send();

But I found in some examples, like this one, that the email could be send using Craft::$app->mailer->send($message) instead of $message->send().

What's the difference between the Mailer and the Message classes? When should I use one instead of the other?

Answer 1

They're both valid options.

$message->send() is a wrapper for Mailer:

https://github.com/yiisoft/yii2/blob/master/framework/mail/BaseMessage.php#L41-L50

It will take an optional Mailer parameter. If one is not passed it, it will default to the default Yii/Craft::$app->mailer and ultimately just call send() on it.