How about Zoho? Their free offering comes with support for custom domains and something like 20 accounts.
As a bonus, you can choose between Zoho.com and Zoho.eu. Both offer the same services, but Zoho.eu is hosted in Europe ender the protection if the various privacy and data protection laws.
Thanks, I will take a look. At first blush it seems like things have changed and the free offering isn't what it used to be -- 5 accounts not 20, and as someone else mentioned, perhaps no custom domain.
But it's worth looking into, because at first glance their lowest paid option fits my general requirements and is only $36/year/user, which is less than ProtonMail.
Yes, it's a few bucks cheaper, but for me Protonmail has that security focus that I worry Zoho don't have. Zoho also provide many other spaid services and that makes me worry about what they have to focus on. Exciting features vs boring security.
I looked into this recently. The free plan doesn't include custom domains anymore. If you had an account before they removed it, you still have it on the free plan.