Can't receive emails to my icloud.com email address. But at least I can send emails perfectly.

Hi everyone,

just a few weeks ago I was waiting for some important emails to my iCloud email address. As I suspected, the sender tried to send them but instead of successful delivery, he received "undeliverable" messages. The sender was a company, so I thought it might be a junk filter or something, but when I tried to send messages to this address from my other email address (outlook.com) those mails were rejected (and I tried sending from all my work and family's and friend's email addresses, same error). Diagnostic code "smtp: 550 5.1.1. user does not exist". However it surely exists, I can send (!) emails from this address without any problems, but I simply can't receive anything. This email address is my Apple ID and I can still use it to log in without any issues (however if I need to recover a password, I don't know how that's going to happen). And of course, the email address is spelled correctly, checked about a thousand times. And this issue is not related to any specific device or the Mail app, I can log in and send emails from any of my devices perfectly. I checked Connection Doctor and account is green, connection and login to server succeeded.

Can anyone recommend me a solution for this, I guess this is not an error on my side, right? Maybe this is a very common issue, but to be honest I haven't seen such an annoying thing before.

Thank you and warmest greetings from Budapest!

Tamas