Persistent Outlook.com 550 5.7.520 AS(4810) outbound blocking across multiple clients

I’m trying to resolve an intermittent outbound sending problem on a personal Hotmail/Outlook.com account.

Messages are being rejected with:

550 5.7.520 – Message blocked because it contains content identified as spam. AS(4810)

The issue is not limited to one recipient, one client, or attachments:

• failures have occurred to both Hotmail and external business-domain recipients;
• Outlook for iPhone has failed;
• Apple Mail has failed;
• desktop/PC sending has also failed intermittently;
• Outlook.com web sometimes succeeds;
• even a completely plain one-word “Test” message has been rejected.

Shortly before the issue began, there was a period of higher-than-normal outbound unsubscribe activity while cleaning up the mailbox. Microsoft then requested additional account verification. That activity has stopped. The account password has since been reset and recent account activity reviewed.

I suspect there may be a service-side outbound anti-spam/reputation restriction or false-positive classification, although I cannot confirm that the earlier unsubscribe activity caused it.

I have complete NDRs, timestamps, Message-IDs and Microsoft filtering correlation IDs available if a Microsoft representative needs them.

I have also attempted to use the normal Outlook.com support route, but the Help pane repeatedly returns “The request is blocked” across multiple browsers, accounts and network paths, including a cellular hotspot. Microsoft Support has already documented the issue in an existing case but could not directly transfer me to the Outlook.com team.

Is there a Microsoft Outlook.com representative who can advise how to get the mailbox’s outbound filtering/reputation status reviewed, or provide the correct escalation path for persistent AS(4810) false positives?