We self host everything ourselves in Latvia (EU country). Mostly in biggest data centre here (DEAC company). One of DEAC data centers is located in former Soviet nuclear bunker so your data is quite safe ;)

Thank you for the answer! Selfhosted in Europe is what I guess I hoped to read. The soviewt bunker is a bit cringy but nice touch. I really consider switching - I just registerd a free address to play with the UI. Is there anything specific I should watch out where the freemium differs from the business plan?

Most of the servers are actually in newest DEAC data centre and not the one in the bunker. The biggest difference I can think of is sending limit. You get the same support even if you are free user (human phone support, support chat, contact form). IMAP access (with custom password) will be enabled only if you validate mobile phone number (Anti spam measure). Our files storage has limited parallel download limit for trial/free users. We also have native iOS/Android apps