Use API instead of smtp

[arashsoheili]

Thanks for this plugin. I think it would benefit if it used the api instead of the smtp user. That would make it faster and allow for multiple email senders from same domain. There is already a Swiftmailer plugin for Mailgun so I wouldn't think this shouldn't be hard (https://github.com/tehplague/swiftmailer-mailgun-bundle).

I'm mainly a Python dev and have some experience with php but not an expert. I'm also new to Symfony as well. But maybe at some point I can try and contribute to this if you are not able to do this. Thanks.

[stars05]

@arashsoheili if you still needed to use mailgun api and Mautic v3, you can use this plugin
https://github.com/stars05/mautic-mailgun-mailer-plugin
It's a similar plugin, but work only with PHP 7.2+ and Mautic v3