iCloud email
i don’t receive messages on my iCloud email even though I have enough storage . I really need it to be working as soon as possible
Send and receive iCloud Mail on all your devices and keep Mail settings up to date - Apple Support
Or else if mail received has large attachments see this article Add an email attachment in Mail on iCloud.com - Apple Support
Read If you can't receive email on your iPhone, iPad, or iPod touch - Apple Support
If iCloud Mail isn't working - Apple Support