Throttling email

nrose
Level 1

Throttling email

My team and I are Marketo developers and appear to see throttling occurring when the system sends an email to the same email address. Is this in the system by design or something that is caused externally? We are trying to do multiple tests and we get the first email, but we do not ever get the follow-up tests to the same email addresses. New email addresses work fine. Thank you in advance.