Delete email addresses from contact record
I know it's seen as bad practice and I know why HubSpot doesn't currently allow it.
But really guys, sometimes we actually do need to delete an email address from a contact record.
I have historical contacts with important notes and history that have never had a valid email address in the email property. Or, someone in our organization entered a bad email address years ago and now it's permanently enshrined on the contact record, causing confusion and bounced marketing emails.
Perhaps when a HubSpot user attempts to clear an email address you can present us with a dire warning and then let the user make that decision themselves. Or, make it an advanced permission that only administrators can enable for themselves.
Either way, deleting the contact record or creating custom properties (as suggested here) are not viable solutions.