[Solved] Hotmail : Undelivered Mail Returned to Sender, Error code : 550 SC-001 (COL004-MC3F19)


I have been running mailinabox for a while, all is well.

There was very low outward output, perhaps a few mails a day. (From half a dozen domains with low traffic).

Then I created a new user by transferring another existing domain name to my box, and the first time they sent a mail to 5 hotmail recipients at the same time, this happened :

De : Mail Delivery System
Envoyé : ‎06-‎12-‎16 08:19
À : ***@domain
Objet : Undelivered Mail Returned to Sender

This is the mail system at host box.*******

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

               The mail system

<******* @ hotmail.com >: host mx2.hotmail.com[] said: 550 SC-001
(COL004-MC6F27) Unfortunately, messages from BOX.IP weren’t sent.
Please contact your Internet service provider since part of their network
is on our block list. You can also refer your provider to
http: // mail.live.com/mail/troubleshooting.aspx#errors. (in reply to MAIL
FROM command)

From then on, no delivery possible to any hotmail adress from any domains on the same box.

Here are the step I took to resolve the problem:
A) check on mailinabox status page that all is green. (ok)
B) check that the user did not in fact send a bunch of spam. (They did not)
C)contact microsoft using this form :

I also tried https://technet.microsoft.com/library/mt661881(v=exchg.150).aspx just in case but it reported that the IP was not blocked by office 365.

After about an hour, I received the following reply :
Dear *********

We have completed reviewing the IP(s) you submitted. The following table contains the results of our investigation.

Conditionally mitigated
Our investigation has determined that the above IP(s) qualify for conditional mitigation. These IP(s) have been unblocked, but may be subject to low daily email limits until they have established a good reputation.

Please note that mitigating this issue does not guarantee that your email will be delivered to a user’s inbox.

Ongoing complaints from users will result in removal of the mitigation.

Mitigation may take 24 - 48 hours to replicate completely throughout our system.

If you feel your issue is not yet resolved, please reply to this email and one of our support team members will contact you for further investigation.

And testing confirm mail is now delivered to hotmail adress, although flagged as junk for now.

Hope this can help others,