Legal Question in Civil Litigation in California

Do you have an agreement with the other side to accept service via email? Have you filed anything electronically with the court? If the answer to either of these questions is yes, then the email was valid service and you have 32 days to respond. If the answer to both questions is no, then the email probably did not qualify as service. You were instead served by mail and have 35 days, unless the court has ordered otherwise or you and the other parties have agreed to a different amount of time.

There are a limited number of other situations where service is allowed (or even required) via email. These include class actions, complex litigation, consolidated actions, etc., if your court's local rules allow electronic service in those cases. I don't know anything about your case, including what court it's in, so I can't say whether any of these provisions applies.

Note that, if this is an unlawful detainer case (an eviction), you really have only five days.