Inability to select which email to send to and no notification for failed sent emails

It's astounding that as any residential or commercial account could have multiple emails, that Zendesk only allows for sending email to the primary email in the account record. If a customer sends us an email from another email on file, Zendesk sees it but we can only respond the to primary and NOT the email sent if it's any other email than the primary. We can't even CC different emails on the same customer record. Incredible. THIS SHOULD BE A BASIC FEATURE of any CRM. Additionally, there's no feedback on failed emails. Textline at least does that.