Yandex Connect? https://yandex.com/support/connect/add-domain.html https://yandex.com/support/connect/add-domain.html Up to 1000 mailboxes per domain https://w

Yandex Connect? https://yandex.com/support/connect/add-domain.html https://yandex.com/support/connect/add-domain.html Up to 1000 mailboxes per domain https://www.yandex.com/support/connect/create-mailbox.html https://www.yandex.com/support/connect/create-mailbox.html For free, for now (though they now have a paid-tier https://360.yandex.com/business/ https://360.yandex.com/business/ which they have integrated somewhat into the legacy and still free Yandex connect)