We are using the API provided by etherscan.io and ethplorer.io in order to import Ethereum Wallet related transactions. These are the best and most reliable APIs on the market. However we are only able to import what they provide over the interface. So unfortunately not all tokens are supported yet and there are some requirements to fulfill, before they list tokens in their API. Also no "Internal Transactions" are being imported by this API provider for the Ethereum Wallet import.
In some cases it is necessary to enter the data manually by yourself. It's easy to find this data on Blockexplorers like etherscan.io.
In addition we provide CSV imports for some software/online wallets (e.g. Trezor, Exodus, Electrum etc.).