How to optimize SmartLead API to increase email open rate when sending large campaigns?

Hello everyone,
I am implementing an automated email marketing campaign using Poly Track SmartLead API, but when sending more than 10,000 emails/day, the open rate drops significantly.
I want to ask:

Is there any way to optimize the API or sending configuration to avoid being spammed?

How should I handle IP/SMTP limits to maintain good domain reputation?

Has anyone tried combining SmartLead with other tracking tools?

Thank you everyone in advance, looking forward to learning more from the community's practical experiences.