Hi Fergus,
Thank you for posting your question in the Microsoft Q&A Forum. I understand that you’re having trouble syncing your New Outlook calendar with Classic Outlook, as well as syncing iCloud with Classic Outlook.
First, go to https://outlook.live.com or https://outlook.office.com and check if your calendar sync works properly. If Outlook on the web works fine, try re-adding your account in both New Outlook and Classic Outlook. If the issue persists, go to Settings > Installed Apps and repair your Outlook/Office installation. For data security, consider creating a backup before troubleshooting.
As a temporary workaround, you can use Outlook on the web and install it as a web app (similar to New Outlook). For instructions, refer to: Use the web version of Outlook like a desktop app
If you still need to contact Microsoft Support:
- Go to Contact Support.
- Type “Outlook syncing problem” > Scroll down and click Contact Support (skip all troubleshooting steps or similar articles if you just want to contact Microsoft Support).
- Sign in if prompted.
- Select Products and Services > Microsoft 365 and Office > Outlook.
- Choose Chat with a support agent in your web browser.
The initial response might not address the problem. So, if your problem persists or you need any assistance, feel free to ask me by clicking "Add Comment". Thanks for your effort.
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Best regards.