Posteo is from Germany and they’re reasonably popular here. Their offer is quite different from Proton, though. If you want full E2E encryption you need to use GPG or S/MIME and handle that yourself (and obviously so does your recipient), so it’s not as batteries included as what Proton offered.
I like their focus on green energy and sustainability though.
Another option like that is mailbox.org. They’re presenting themselves as a bit more business-like.
I honestly just use browser bookmarks. That’s always been enough for me. Firefox can sync them too, so that takes care of backups as well.
For anything that needs special attention, I create a todo item with the link in org-mode.