What are mining or transaction fees?
Each time you send a blockchain asset you must include a tiny transaction fee to ensure your payment is processed and reaches the destination. These fees are paid to each assets network (Bitcoin, Ethereum, etc.). They are not kept by Exodus.
If the asset network is busy, which has been the case for Bitcoin since late-2016, these fees are typically higher. You can always see the fee, along with the corresponding asset amount, in the lower right of the send dialog.
If you are looking to minimize transaction fees less popular networks will always have lower transaction fees. For example Litecoin will be less than Bitcoin.