A new domain with no sending history has zero reputation with ISPs yet, so this is expected to some degree — but how you ramp it matters a lot, similar to what we covered in this earlier deliverability thread about sudden volume changes. For a brand-new domain specifically, you want a deliberate warm-up: start at roughly 20–30 emails/day for the first week, then increase gradually (not more than ~50% per week) over 4–6 weeks before reaching full volume. Jumping straight to your old domain's volume on a domain with no history is one of the fastest ways to get flagged.