Hi
On our site, we got Mailpoet working with Sparkpost using the Sparkpost plugin (https://www.ads-software.com/support/plugin/sparkpost). To do this we:
1. Configured the Sparkpost plugin to use the ‘HTTP API (Default)’ send method, gave it our API key, and checked the checkbox to ‘Send email using SparkPost’. (You can send a test message at the bottom of this settings page to check that this is working).
2. Configured MailPoet. On the MailPoet settings ‘Send with…’ tab, we chose to send with ‘Your own website’ and chose Delivery method ‘WP mail’ – behind the scenes this means that emails actually get sent by the SparkPost API. (You can send a test message on this page too).
3. Once we’d got this far, we found that though the emails were being sent, they were in the wrong format. This seems to be just a bug in MailPoet, which I raised on this forum in this post: https://www.ads-software.com/support/topic/integraiton-with-sparkpost-http-api?replies=3#post-8353435 – this post also shows how we fixed it ourselves on our site. Having done this, everything seems to be working fine!
This last step involves making a one-line change to a code file in the MailPoet plugin on your website. If you’re not happy or able to do this, hopefully MailPoet will resolve this issue themselves and release an updated version of their plugin which would then just work with SparkPost.
Hope this works for you.