If you have trouble receiving email in Mail on iCloud.com
If you’re having trouble receiving email with iCloud Mail, try the following:
If you turn on email forwarding and automatically delete messages after forwarding, you might not see messages in your iCloud inbox. To check, tap the Action pop-up menu in the sidebar, choose Preferences, and see if “Forward my email to” and “Delete messages after forwarding” are selected. If you make changes, make sure to tap Done to save them. See Automatically forward email in Mail on iCloud.com.
You might have a rule that filters messages to a folder that’s not your inbox. See Set up rules to filter email in Mail on iCloud.com.
Make sure you’re using a browser recommended in the Apple Support article System requirements for iCloud.
If you’re not seeing email from a particular sender, check your iCloud Mail rules to make sure you don’t have a rule set up to delete messages from that sender.
Check the Junk folder for messages that were incorrectly marked as junk. See Manage junk mail in Mail on iCloud.com.