I have my demo account now, but I would like to test with the sendinblue plugin. Is there a way to install so that I can test the behavior?
There is no support for SendInBlue REST API yet (it is planned for September or October). Currently, SendInBlue is supported through PHPMailer SMTP Service, and you can select it from PHPMailer panel, and make sure to add SendInBlue SMTP credentials.
So that we are clear, I can still use their api directly to send to sendinblue bypassing your queue, but any action which simply uses the wp_mail interface to send an email would be queued and sent through your plugin and eventually sendinblue, correct?
Essentially yes. But, you can’t use my plugin with other email plugins, because most of them are written so that my plugin is bypassed. My plugin is the only email handling plugin that doesn’t override any WordPress functions, while SendInBlue API plugin they made (and all others) are replacing WordPress functions, and my plugin can’t do anything because of that, my plugin depends on the WordPress functions being WordPress functions.
You can use my plugin with SendInBlue but through SendInBlue SMTP service and not SendInBlue REST API. But, REST API support for SendInBlue is coming in the form of a free addon for GD Mail Queue Pro. In terms of speed/reliability SendInBlue claims that SMPT and REST API are equal. The only problem might be your own server SMTP limits if they are set in the first place, and most shared hosting servers do have them.