In Yuki, it is possible to have email (containing documents) from your own email box automatically forwarded to the email address for documents of your administration in Yuki.

If you are using a Microsoft email account, invoices may not arrive in Yuki and you will receive an email with the following message:

5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)

This error message indicates that external email forwarding is not allowed.

So in your Microsoft email account settings, it is set that it is not allowed to automatically forward email to external recipients (in this case, your Yuki email address).

For more information, see Microsoft's website: 

Yuki recommends that you contact the mail server provider.