Receive "Mail Delivery Status Notification (Delay)" on Microsoft email address

Receive "Mail Delivery Status Notification (Delay)" on Microsoft email address

Hi,

Until 4 days ago, everything was working well with my Account Confirmation Emails. Customers where able to receive mails almost instantly.

But these last 4 days, for every customer with an address in 'live.com' 'outlook.com' and 'hotmail.com' I reveive back an email with this subject: "Mail Delivery Status Notification (Delay)". and my customers do not receive the emails.

I did as the mail said and waited 4 days as said in the mail: Message will be retried for 4 more day(s) "

But unfortunatly my emails are not delivered after 4 days.

Why does that happen? How can I fix it? in the end it's quite a lot of money lost so it's quite urgent.

Thanks in advance