gmail reports "blocked" when sending to icloud

You can see whether your messages in Mail are being automatically forwarded to another email address and easily disable forwarding.

1. Sign in to iCloud at https://www.icloud.com with your Apple ID username and password. If necessary, enter the two-factor authentication code.
2. Click Mail, then click the Settings button  at the top of the Mailboxes list, then choose Preferences.
3. In the General tab, see whether “Forward my email to” is selected and whom it’s being forwarded to. If necessary, remove the forwarding address and stop forwarding mail messages.

from the article Safely manage how you forward content - Apple Support