Depending on the third-party service, GD Mail Queue supports SMTP and REST API methods to connect to various services and send emails through them. Most email sending websites support sending of transactional emails (these emails can be anything coming from your website), not only email campaigns. And, most services support the use of SMTP Relay, making the integration easier.
But, SMTP might not be a good solution for everyone, so there is a way of using REST API libraries and services own API’s to send emails outside of the SMTP mailing system. Implementing REST API can be complex, depending on the service, and GD Mail Queue Pro, for each REST API supported service has an addon (a smaller plugin that integrates into the main plugin). Addons are used because API libraries can be huge (AWS SES is 12MB), and there is no need to ship each API with the main plugin, or it would be a huge plugin to prepare and work with.
|Service Name||SMTP||REST API|
|Gmail||No||Yes (Free Addon)|
|AWS SES||Yes||Yes (Free Addon)|
|SendInBlue||Yes||Yes (Free Addon)|
|Mailgun||Yes||Yes (Free Addon)|
|MailJet||Yes||Yes (Free Addon)|
This is not the final list, it is last updated with the release of GD Mail Queue Pro 4.2. If you want to suggest more services to support directly, open a new ticket in the support forum.