We use the Automated Clearing House (ACH) secure network for external account transfers. The ACH network is the same one used by the Federal Reserve to clear checks between financial institutions. The funds are sent similar to how direct deposits and automatic payments are made on loans and mortgages. 

To give you an idea on how the money is moved, here's a quick summary:

1. You provide us with the transfer details, including the account and routing numbers.
2. We submit the request to the ACH.
3. The ACH sends the funds to the financial institution specified by the routing number provided.
4. The other bank deposits the money using the account number provided.