Sure! A great example is the actual code we are using now. We are based on the Laravel framework so here is the driver code laravel uses. <a href="https:&#x2F;&#x2F;github.com&#x2F;laravel&#x2F;framework&#x2F;tree&#x2F;5.2&#x2F;src&#x2F;Illuminate&#x2F;Mail&#x2F;Transport" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;laravel&#x2F;framework&#x2F;tree&#x2F;5.2&#x2F;src&#x2F;Illuminate...</a><p>You&#x27;ll notice there is an abstract class &quot;Transport.php&quot; which declares certain methods (via the Swift_Transport interface class) that the &quot;MandrillTransport&quot;, &quot;MailgunTransport&quot; and the &quot;SesTransport&quot; must all implement.<p>&gt; I think case in point, free is not forever in SaaS business.<p>Our account &amp; our customers&#x27; accounts were all paid. Some of them send up to 500,000 emails each per month. I would have been fine with them getting rid of the free tier, its the TOS change for marketing emails that killed our use with them.