Not a e-mail provider but related: Addy.io accepts Monero :)

Runbox accepts crypto thru a third-party integration, although not XMR last I knew ... BTC, LTC etc

@HardenedSteel this is a niche still awaiting for its entrepreneur.

Proton accepts btc (sigh (put +1 to the column that argues for them being a honeypot)). You might use trocador to exchange from btc to xmr and make your payment.

But, again, some sort of email service that takes XMR in exchange of service would be good. The operators of the email service can even use the XMR payment as a sort of counter-spam measure against bot accounts, and spam senders. The service can also use "Mullvad-style" random digits per the customer in order to track their XMR payments for the service, and demand no personally identifiable information, at all.

Not direct, but Tutanota via Proxy Sto.re accepts monero, and they have plans to add direct monero support "eventually".

https://digitalgoods.proxysto.re/en

Of the privacy guides encrypted email providers, only Tutanota has any Monero option at all. https://www.privacyguides.org/en/email/

Although not Monero-centric nor commercial, disroot + Monero donation = custom domain(s) is probably possible.

(Like 2 years ago, there was also CTemplar, but no longer.)