PHPMailer Service: PepiPost SMTP Server
Debug email sending for different services and engines
Does the plugin supports other SMTP sending plugins?
But, GD Mail Queue has support for SMTP email sending, and you can add your SMTP server information for plugin to use for all emails and/or queue emails. If you need to use REST API for email sending or you want to use predefined SMTP sending services through PHPMailer, GD Mail Queue Pro supports several popular email services using official REST API libraries and SMTP sending to.