In a bowl, whisk together eggs, buttermilk, mustard, 1.5 tablespoons Cajun seasoning, salt, and pepper. Add shrimp, toss to coat, and marinate for 20 minutes.
Combine flour, cornmeal, and remaining 1.5 tablespoons Cajun seasoning with salt to taste in a shallow dish. Dredge the marinated shrimp in the flour mixture, shaking off excess.
Heat oil in a deep fryer or large skillet to 350°F. Fry the shrimp in batches until golden brown and cooked through, about 2-5 minutes. Drain on paper towels.