Hi @Paul Envizzo!
This is a bit of a tricky one because it’s not just about the number of emails that are sent, but also the number of people on the receiving end who then flag that email as Spam. Different email providers (Gmail, Outlook, etc) will have different criteria for treating an email as spam; there’s no fixed number of emails that will cause email providers to flag an email address as a spam provider. I’m not an expert, but I’ve heard cases where if more than 2-3% of recipients flag as spam the whole email domain (if you’re not using a generic @gmail.com) can be flagged as spam.
On the whole, it’s better to use a bulk or transactional email provider like MailChimp (good for newsletters, etc), SendGrid or Mailjet (both transactional email services).
Depending on the reason that you’re sending the emails and how often you plan to send them, I also advise you to check the Zapier Terms of Service to make sure that you aren’t in breach of them.