Hello MRZ1975,
Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with finding all of your iCloud mail. You can read your iCloud mail as described here: Read email in Mail on iCloud.com - Apple Support
You can find information about your mail folders in iCloud here as well:
"Organize email with folders in Mail on iCloud.com
iCloud includes seven default Mail folders: Inbox, VIP, Drafts, Sent, Archive, Trash, and Junk. You can create additional folders and subfolders to organize your email.
When you create additional folders, they’re visible on any device that has Mail turned on in iCloud settings.
To work with folders, make sure the Mailboxes list is visible."
We hope this helps.
Cheers!