Have a look at Yandex Mail.
It is a free feature-rich email service with unlimited mailbox size. It has two-factor authentication and login history to prevent hacking. It scans all incoming mail for both spam, phishing, and malware.
Does it's SMTP work well? They recommend not to use their SMTP servers for third party operationsI also recommend Yandex mail and yes you can use your own domain for email.
it worked for my WordPress with both Yandex mail SMTP plugin and WP Mail SMTP Pro. I also used it in Gmail mobile app.Does it's SMTP work well? They recommend not to use their SMTP servers for third party operations