Hi there,
No worries about writing English :-)
So the old email addresses are working fine, the new ones are not working correctly.
Are they both on the same domain name?
Keep in mind that when you enable the email service for a domain name, the DNS records required for our email service to function correctly, are created just then.
It takes 4-24 hours after that for email to start working correctly. However, if the email service was already enabled for this domain name, that shouldn't be the issue.
Please read this article: https://site.nl/helpdesk/artikel/kun-je-niet-bij-je-e-mailadres-volg-deze-handleiding-73
(on the top of the page you can choose 'English' as your preferred language)
In that article, especially pay attention to these sections of the article:
'3. Recent email service activation'
'5. Does the email address exist?'
I think one of these two might be the issue.
Sometimes users forget to click the green Save icon when creating an email address.