rDNS and Shopify mail server

[DiegoDD]

Hello,
I use Shopify with a custom third-party domain.
To send newsletters to my subscribers, I use Shopify's mail service.
I need to configure a reverse DNS (rDNS) to prevent my emails from being marked as spam.
I found this guide that explains all the steps to configure reverse DNS (although I don't use DNS Made Easy, I feel like the guide can help me).

However, I don't know how I can find the IP address of Shopify's mail server. Can anyone help me or have any experience with setting up rDNS?

Thanks in advance