Welcome to EMD!
Let us say your custom domain is example.com. When someone sends you an email at rain@example.com, the sending SMTP server must first look up the MX entry in the DNS records for the email domain (example.com). The MX points to the IP address of the email server which can accept mail for that domain.
But Gmail currently knows nothing about your domain. If you point your MX to the Gmail incoming server, the Gmail server will refuse to accept the message. There are three basic ways to get around this issue if you insist on using Gmail to read your own domain email:
- Forwarding: Some domain hosts offer an email forwarding service which forwards emails sent to your private domain to another email address. In this case that would be your Gmail address. However, email systems now use methods such as DMARC to verify the authenticity of incoming messages. DMARC uses SPF to verify that the sending server is allowed by the email domain DNS records to send mail, and DKIM is used to verify that the message was not corrupted by cryptographically signing a header. In addition, DMARC requires that the email From address is aligned with the SMTP envelope FROM address. When an email is forwarded, this alignment is not possible. So email forwarding may prevent Gmail from accepting the message without treating it as spam.
- You could set up an email system which stored incoming messages, then use Gmail to read them using POP or some other technique.
- I think you can use a Google Workspace (paid) account to handle your custom domain email. This would be the preferred method. I do nott have such an account and so cannot help you more with that service, since I use Fastmail.com to handle all of my own domain email. You might post in the Google Gmail forum at EMD to get more comments about use of Gmail with your personal domain.
You probably want to also send emails from Gmail using your own domain name. I think that a Google Workspace account is probably the best way to meet all of your needs.
Again, I personally do not want to let Gmail have access to my main email, so for this (and other reasons) I use Fastmail for my personal domain email. Many other competitive solutions are also available. You can decide which service meets your needs.
Bill