Here is my advice for the New Year (and I think it’s worth doing some planning for this in advance – 27th to 30th December seems like an ideal time).
Create a folder in your email setup called previous_years (or something similar). Inside that folder create one folder called 2025, one called 2024, one called 2023 etc. Now move all the messages from your Sent and Inbox folders into these new folders depending on when you sent or received them.
Now you can start 2026 with empty Sent and Inbox folders. See how long you can keep them empty (by moving anything you send or receive into folders specifically for the people that you send a message to or receive a message from). But crucially – do not be hard on yourself if you run out of steam doing this. It’s not easy to keep it up. I used to manage about three months. Now it’s more like nine.