Help! I'm blocked at Microsoft! What do I do?

Keep in mind that Microsoft has two separate mail systems: OLC (Outlook Consumer) which you might call Hotmail, and corporate mail hosting, the mail systems associated with their Office 365 service. The two systems have separate processes with regard to requesting to be unblocked. Here's links for both.

Microsoft OLC: If you are trying to send mail to,,, or any other Microsoft OLC (Outlook Consumer) domain and you're seeing this bounce message:

5.7.1 (delivery not authorized) Unfortunately, messages from [] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to []"

Or if you are seeing this deferral/delay message:

451 4.7.650 The mail server [] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see (S843) []

Then you've got a reputation issue at Microsoft OLC (Hotmail/ to address. Why? What caused it? Multiple things can make this happen. A few of the possible reasons are: Too many complaints. A spike in email send volume. Too many attempted deliveries to invalid addresses (which can appear to Microsoft to be a dictionary attack). Too many negative SRD votes. And possibly other things. You might want to engage a deliverability consultant to review your email marketing methodology and data to identify any possible issues. 

When you're ready to reach out to Microsoft (OLC) to request that they either stop blocking you or that they should allow you to send more mail to their users, you'll want to go here and fill out this form.

For more guidance and understanding around blocking issues and deliverability best practices for Microsoft OLC (Hotmail), Microsoft publishes a Postmaster Site for, though some of the info looks as though it may possibly be out of date. 

Microsoft Office 365: If you're trying to send email to corporate domains that are hosted by Microsoft and you're seeing this bounce message:

5.7.606 (undefined status) Access denied, banned sending IP []. To request removal from this list please visit and follow the directions. For more information please go to AS(1430) []"

Then you've got a reputation issue at Microsoft Office 365, the corporate mail hosting side of things. That's different than Hotmail. Both systems run on the same back-end platform, but it's not clear to me if the spam filters are exactly the same-- I suspect they are not. Generally speaking, the same kinds of sending issues can cause blocking on either side, but I have my doubts that the thresholds and mechanisms and monitors would be exactly the same.

When you're ready to reach out to Microsoft (Office 365) to request that they stop blocking you, you'll want to go here and fill out this form.

Sergey Syerkin, Head of Email Delivery Operations at MailerQ was kind enough to share this additional information for Microsoft Office 365: If you're having a content-related issue and/or a high "SCL" (Spam Confidence Level) issue with Office 365, you may need to utilize the false positive submission process documented here. Thanks, Sergey!
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