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Email Deliverability to Outlook / Hotmail / MSN

Written by: on 23 July 2021 10:02 AM 23 July 2021 10:02 AM
If you are getting bounce back messages when sending emails from your server to Outlook, Hotmail or MSN, and the bounce back contains the following:

550 5.7.1 Unfortunately, messages from [x.x.x.x] 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

This is because your IP has been blocked by Microsoft. This usually occurs if:
1. Your server has been sending SPAM (check your mail queue to ensure it's not currently sending SPAM).
2. You have mailboxes on your server that forward to Outlook, Hotmail or MSN. Microsoft does not distinguish between forwarding SPAM and originating SPAM, this means if you forward all email sent to your address to a Microsoft address, and someone sends you SPAM to, Microsoft will block you for it. Therefore we do not recommend under any circumstances forwarding email to Microsoft addresses (or GMail as Google behaves in a similar manner) from your domain email accounts.

Once you have checked and stopped both of the above, you can request removal of your server IP address from Microsoft, see:

They usually take 6-24 hours to begin mitigation.
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