def extract_domains(email_addresses):
    """
    Returns a list of email domains extracted from list of email addresses
    Parameters
    ----------
    email_addresses: list, required
        Email addresses are dict of type { "address" : "recipient1@domain.test" }
    Returns
    -------
    list
        list of email domains
    """
    domains = set()
    for address in email_addresses:
        domains.add(address['address'].lower().split('@')[1])
    return domains