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Microsoft's Outlook.com is one of the largest email providers in the world and anybody who sends email to customers will encounter plenty of outlook.com, hotmail.com or live.com addresses. As such, Microsoft has to deal with a lot of spam for all those billions of emails it processes and sometimes the spam detection is a bit overzealous. It doesn't take much for your server's IP address to be blacklisted, or you might even inherit a blacklisting from the previous owner of the IP address assigned to your newly commissioned server. Then you get the 550 SC-001 error.
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