Email is designed to interrupt you. Every notification pulls your attention away from what you are doing. This constant switching fragments your focus and makes deep work impossible.
Instead of checking email constantly, schedule specific times. You might check it three times a day: morning, midday, and evening. Or twice: morning and afternoon. The frequency does not matter as much as the consistency.
During your email batches, process everything. Reply, file, or delete. Then close your email and do not check it again until your next scheduled time. This gives you long stretches of uninterrupted time for focused work.
Set your email schedule today. Choose two or three times when you will check email. Turn off notifications. Then notice how much more focused you become when email is not constantly interrupting you.