When adding multiple external email addresses as support addresses in my account, do I need to make a new Zendesk address for each external email address?
No, you do not need a new Zendesk support address for each of the external email addresses you are configuring. All external emails can be forwarded to the same Zendesk support address,
email@example.com, where the subdomain refers to your specific account's name.
For more information, see the article: Forwarding incoming email to Zendesk Support.