The bigger freemail companies are more regulated and even they aren't regulated enough. I've had issues with GMX in the past which is the same company as mail.com albeit this was a long time ago, however current reviews for mail.com seem to be the same as I would have reviewed 10 years ago for GMX.https://www.sitejabber.com/reviews/www.mail.com
I don't use any webmail system except for testing, my emails are all stored on my desktop using POP3 accounts and Mozilla Thunderbird, which I also doubly back-up, I have emails going back 17 years.
After losing loads of emails on my old Netscape webmail account I realised that if I wanted anything kept, I needed to store it myself.
Even my own email servers are fed through Thunderbird on my desktop to store and backup rather than doing it at the server end.