I’ve been using their email forwarding (paid) for a few years now. Great for side projects and any random domain I register. I immediately catch all to a [email protected] so I have all my email in one place. Most of its bullshit and spam, but the few interesting reach outs are usually worth it.
I know these because I have spent time looking the past week for getting off Outlook.com. I've basically settled on Runbox.com as it seems to be the most established and stable.
* Android app sending incomplete emails. Sometimes the email would just be truncated once I checked it in my sent folder. They claim this is fixed in their Beta app, but I have not confirmed.
* A large (12-ish-GB) file repeatedly failing to download from Proton Drive, both through the web interface and their desktop app. Took many attempts before it finally worked through the web UI. So... don't use Drive for critical backups without other copies around.
Both of the above were encountered in the last year. Aside form that I've had no other problems that I can remember in all these years, so I've been generally happy with it.
Can anyone recommend a privacy focused email provider that can run free or cheap custom domains?