=== import preview ===
{
    "filename": "recipients.csv",
    "headers": [
        "Email",
        "FirstName",
        "LastName",
        "CompanyName"
    ],
    "summary": {
        "total_imported": 5,
        "valid_recipients": 2,
        "invalid_recipients": 1,
        "duplicate_recipients": 1,
        "suppressed_recipients": 1,
        "bounced_recipients": 0,
        "errors": []
    },
    "valid_sample": [
        {
            "email": "alice@example.com",
            "first_name": "Alice",
            "last_name": "Smith",
            "company_name": "Acme Corp",
            "company_phone": "",
            "customer_email": "alice@example.com",
            "custom_fields": {}
        },
        {
            "email": "bob@example.com",
            "first_name": "Bob",
            "last_name": "Jones",
            "company_name": "Beta LLC",
            "company_phone": "",
            "customer_email": "bob@example.com",
            "custom_fields": {}
        }
    ],
    "invalid_sample": [
        {
            "email": "not-an-email",