Mac Mail has 150,000 emails to contend with and it's slowing down the MacBook

Hello-

My Mac Mail currently stores and indexes 150,000 emails, which are redundantly stored on a server. I believe this is slowing down both Mac Mail and the machine. What is the best / most efficient / etc way to improve this? Preferably by having Mac Mail automatically remove emails older than x number of months from local storage, and by not syncing emails older than x months old. Is this possible?

Thanks!