We've had good luck with MailWizz. PHP-based, but has a good plugin system and does some pre-processing prior to sending in a way that improves deliverability.

We've had good luck with MailWizz. PHP-based, but has a good plugin system and does some pre-processing prior to sending in a way that improves deliverability. It's not a speed demon out of the box with default settings, but there's a lot of documentation on how to improve performance. Touble-free API integration with most of the big API-driven services like SES, Mailgun, etc., and works well with self-hosted SMTP too. It's available on (sigh) Code Canyon. (Disclaimer: I own a few licenses and use Mailwizz to send about 1-1.5 million emails a month, but I don't get anything for saying I like the product.)