Using custom domain with free Gmail accounts

TL;DR We are using our custom domains via Gmail interface through SMTP2GO (free) SMTP Server to send emails, and Cloudflare (free) Email Routing to receive emails. The goal: free custom domains for our emails on the free Gmail client (send and receive). When we were using Google Domains with Gmail, the two services worked well together. We moved on from Google Domains and I set up our hosting on…