I have the same issue. No custom domains for email. I use hide my email for certain mailing lists.
Set up rules for email sent to (hide my email address 1) move to folder X.
email moves to folder x, I see there is 1 unread email - No notification sound though.
Turning on a rule ends notification sounds for any email that falls into the rule. Emails that just come to my inbox without a rule, hide my email or not, get notification sounds.
There seems to be a problem with how Apple manages notification triggers. Notification sounds should be triggered regardless if the email is processed by a rule or not. This might have something to do with Apple requiring rules to be applied in the cloud for them to be correctly applied across more than 1 device.
I would value Apple giving email a functional review and include reviewing the encryption / security.
A feature I would appreciate is a “Button” to export email in an email folder to a folder on Mac as individual PDF’s.
anyhow.. notification issues are still present when rules are applied, would be great to see this resolved.