In New Outlook, the handling of spam or bulk email may differ from what you experienced in Outlook 2016. While you have a Bulk folder in New Outlook, it might not be automatically populated with spam emails from your Yahoo Mail account. This could be due to the way New Outlook integrates with your email accounts and how it manages spam filtering.
If spam emails from your Yahoo Mail account are not appearing in the Bulk folder or any other folder in New Outlook, it is possible that they are being filtered out by Yahoo's own spam filtering system and not being synced to Outlook. Therefore, you may need to check your Yahoo Mail account separately to ensure you don't miss any important emails that could be classified as spam.
For a more integrated experience, you might want to check the spam settings in both your Yahoo Mail and New Outlook to ensure they are configured correctly to manage spam effectively.
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