Check out Migadu. They are a Swiss company and offer unlimited domains and mailboxes for just $4 a month. The only drawback is that you can only send 100 emails a day combined from all your email addresses. Good for personal use I guess.

They also have higher tiers if you want to send more emails.

https://www.migadu.com/en/pricing.html

Omg! That's absolutely exactly what I need for all my sites. Thank you!

And it gets even better

Before paying a cent, all our users evaluate Migadu through our free, unlimited trial plan. The free plan supports one email domain, unlimited number of mailboxes, 1 Gigabyte of email storage and 10 outgoing messages per day which include a discreet signature "Sent via Migadu" at the bottom of each message.

If the limits of the free trial plan fit your needs and you do not mind the signature, you are welcome to stay on the free plan forever. There is no time limit. Upgrade only when ready and convinced.

I mean I rarely sent more than 10 email on my personal account. It is more of a receiving end. And this is awesome.

Edit: This needs to get submitted to HN in later hours for more exposure.

I just switched off gmail in favor of FastMail

I have grand-fathered accounts for my custom domains from when it was free, but I still just forward and delegate to my free non GSuite personal gmail. If Google ever kills those I'm gonna just move the domains to a different mail provider and forward to my personal gmail the same way.

I just switched from GSuite to https://www.pobox.com. For $20 a year they manage your email address and forward anything sent to it to another account. I have a gmail free account set up to send emails via smtp through pobox, which works great. It's the service a lot of open-source people use, like gitster.

EDIT: Looks like https://improvmx.com do the same thing, but for free.

To just forward emails from your private domain, you can transfer the domain to NameCheap and use their free email forwarding service.

Exchange Online is $4/user/month with annual billing.