I have been using mailbox.org for a few years and no complaints. I don't think the web UI is amazing but I use it via Thunderbird so it doesn't affect me.
If you use your own email client and your own domain name, you don't really need to worry about UI with email providers at all (as long as your provider supports those features). And your own domain name makes it easy to move around in future if you need to.
I don't really have any plans to move away from mailbox.org, though I just saw the post about Thunderbird offering an email service in the future. That might actually prompt me to move as I'd like to support the makers of a FOSS email client I've been happily using for years.
If you use your own email client and your own domain name, you don't really need to worry about UI with email providers at all (as long as your provider supports those features). And your own domain name makes it easy to move around in future if you need to.
I don't really have any plans to move away from mailbox.org, though I just saw the post about Thunderbird offering an email service in the future. That might actually prompt me to move as I'd like to support the makers of a FOSS email client I've been happily using for years.