Soggy Italian calzones
Possible causes of soggy calzones and their fixes.

The oven is too hot. It seems counter-intuitive, but this browns the crust to golden perfection before the internal temp of the stuffing reaches an ideal point. It won't get hot enough for long enough to steam out the sauce and ingredients. Cook at a lower temp for longer and broil to perfection if needed. 

The ingredients have too much water. If you're tossing a ton of onion, mushrooms, green pepper, tomatoes, etc into the diaper, you'll have to adjust your cooking parameters compared to drier protein stuffings. You might want to saute the ingredients before incorporation to give them a head start on temp and water loss.

The sauce is too runny or under-cooked at the start. Make sure to use a thicker sauce, even than with pizza. Pan-heating commercial sauce before baking will help. You can even turn spaghetti sauce into calzone sauce if you simmer it long enough.

The crust is too greasy. While it tastes and looks great, if the crust is too greasy, it can seal in steam instead of allowing it to permeate and escape. While eventually the moisture will find a way out with swelling/bubbling and "geysering", a lot of water vapor will condense on the non-leaky spots and drip to the bottom; think about the sweaty lid of a rice cooker. You can also simply add vent slits in the crust (like buttery pie crusts often sport) if you have otherwise-good results with your current recipe.

Generic methods of reducing moisture include baking/resting on a rack instead of a plate/pan, opening sooner after cooking to allow poofs of steam to escape before it becomes liquid (many restaurants serve them split in half), and resting them upside down to hide some of the juice in the thicker less-soaked top crust.