I'm still struggling to understand the decision making here though: this is a premium product pricing itself above the various GSuite/Exchange/Online/Fastmail, and demanding a significant time investment from users (for the whitelisting). There is of course nothing wrong with that, and I really like the idea of a premium, well crafted email system.
However, the lack of archive import (and of sync'ing to alternate email addresses it seems?) seems puzzling here.
I'm not sure that the Venn diagram intersection of people who really care about email but do not require import of their current archives is a large enough market to go after.
I have a small-ish archive (15 years) and any service that wasn't able to work with is a nonstarter for me. I imagine while not the most common situation, we are talking about premium email here...