Recently my client has encountered problem that all their email sent to hotmail.com got bounced back immediately with the following error message.

Server response to MAIL FROM:
550 SC-001 (BAY004-MC4F44) Unfortunately, messages from xxx.xxx.xxx.xx 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.

It turns out their email server IP got blacklisted by hotmail.com due to suspicious spam activities, given the fast even their IP isn’t listed on any of the RBL anti-spam database.

The solution is quite straight forward but does with a bit of luck, simply fill in the form and PRAY Microsoft will get back to you shortly. (and they did recently, average reply time is about 10-30 mins)

The following is the actual reply from Microsoft:

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

Conditionally mitigated
xxx.xxx.xxx.xxx, xxx.xxx.xxx.xxx, xxx.xxx.xxx.xxx,

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.

Regardless of the deliverability status, Outlook.com recommends that all senders join two free programs that provide visibility into the Outlook.com traffic on your sending IP(s), the sending IP reputation with Outlook.com and the Outlook.com user complaint rates.

Of course, the above is just the normal scenario. Worst case, your email to hotmail.com could be never bounced back but disappeared totally in darkness.

After filled in the above form, you get a very discouraging reply from Microsoft saying your IP cannot be unblocked.

Not qualified for mitigation
xxx.xxx.xxx.xxx
Our investigation has determined that the above IP(s) do not qualify for mitigation.

Please ensure your emails comply with the Outlook.com policies, practices and guidelines found here: http://mail.live.com/mail/policies.aspx.

To have Deliverability Support investigate further, please reply to this email with a detailed description of the problem you are having, including specific error messages, and an agent will contact you.

Don’t worry, the next step is to reply to that particular email and explain the situation in detail and politely, normally, Microsoft will grand you the rights to unblock your IP again.

My name is xxx and I work with the Outlook.com Deliverability Support Team.

Recent activity coming from your IP (xxx.xxx.xxx.xxx) has been flagged by our system as suspicious, causing your IP to become blocked. I have conducted an investigation into the emails originating from your IP space and have implemented mitigation for your deliverability problem. This process may take 24 – 48 hours to replicate completely throughout our system.

Please note that lifting the block does not guarantee that your email will be delivered to a user’s inbox. However, here are some things that can help you with delivery: