That was a turn off for me personally. While I think more expensive per user (but free for up to 150 emails per day without your own domain name), ProtonMail has "Proton Bridge" that works wonderfully for me on Windows 7/11. It gives you what the name suggest, its a bridge between your cloud encrypted emails and sets up local SMTP that you can connect any program to (I have Thunderbird and Outlook). Haven't had any issues at all.