Got a new custom domain like domain.com ? but your registrar offers only a paid mail service with and/or a simple forward for free ? doesn't matter! forget it and get your working Gmail account with your @domain.com right now for free !
After your register a new domain, your registrar/DNS host will show a lot of configurable things, like A, AAAA, CNAME and MX records. What is used for email is called MX, the MX (Mail exchanger) record holds the mail server IP/DNS which will handle all the emails to your @domain.com. To get a working Gmail with your domain you need put the Gmail MX records there, unfortunately GMail doesn't allow this, but the Zoho mail service yes!
Zoho.com is a free mail server like Gmail, which supports MX record. But how do I receive emails in my Gmail account? Gmail, like Zoho supports POP3 and SMTP server configurations, which will be the bridge between the two services.
Create a Gmail account, if you have one already, you don't need create another, because, as you will see, they can work isolated and without touch each other in the same account. Now create a Zoho account and point your DNS host MX records to the Zoho ones (link). Your DNS host will show something like this:
Now add the Zoho POP3 and SMTP servers into your Gmail account (link):