Firebase Authentication verification email cannot be received by other email domain

Hi,

i'm working on a next js web app and i am using Firebase Authentication. I just setup a custom email domain inside "Email Address Verification". The problem is when someone sign-up using other email such as @ icloud.com or a business email address the users are not receiving their verification email from firebase. Only gmail.com works properly.

Do you have any idea how to fix this? DMARC, SPF, DKIM are already implemented

Thank you