only happens when i open mail box

Hi @mightydanp. If you have the Steam version, try verifying the game integrity to reset your game files to default. This won't affect SMAPI mods, but any XNB mods will be removed.

alright i have and when i add the more crops mod is when i cannot access my mail box

I suggest reporting the problem to the More Crops mod author to look into it. :)