Tutorial · C#

Verify Email Addresses with C#

Real-time email verification in .NET using HttpClient and System.Text.Json — no external packages needed.

GET https://api.validemail.net/ 1 credit per verification .NET 6+

1

Verify an email address

Send a GET request with the email and your API token. The helper below also handles interim Unknown results by waiting RetryAfterSeconds and retrying automatically.

C#

using System.Net.Http.Json;

const string ApiUrl = "https://api.validemail.net/";
const string ApiKey = "YOUR_API_KEY"; // find it in your ValidEmail dashboard

using var client = new HttpClient { Timeout = TimeSpan.FromSeconds(90) };

var result = await VerifyEmailAsync("someone@example.com");

Console.WriteLine($"Valid:  {result.IsValid}");
Console.WriteLine($"Score:  {result.Score}");
Console.WriteLine($"State:  {result.State}");
Console.WriteLine($"Reason: {result.Reason}");

if (result.IsValid && result.Score >= 80)
{
    Console.WriteLine("Safe to send.");
}

async Task<VerificationResult> VerifyEmailAsync(string email, int maxRetries = 3)
{
    VerificationResult? result = null;

    for (var attempt = 0; attempt < maxRetries; attempt++)
    {
        var url = $"{ApiUrl}?email={Uri.EscapeDataString(email)}&token={ApiKey}";
        result = await client.GetFromJsonAsync<VerificationResult>(url)
            ?? throw new InvalidOperationException("Empty response.");

        // "Unknown" means the verification is still in progress (e.g. greylisting).
        if (result.State == "Unknown" && result.RetryAfterSeconds is int retryAfter)
        {
            await Task.Delay(TimeSpan.FromSeconds(retryAfter));
            continue;
        }

        return result;
    }

    return result!; // still pending after maxRetries — treat as risky
}

public sealed record VerificationResult(
    bool IsValid,
    int Score,
    string Email,
    string State,
    string Reason,
    string Domain,
    bool Free,
    bool Role,
    bool Disposable,
    bool AcceptAll,
    bool Tag,
    string MXRecord,
    int? RetryAfterSeconds,
    List<AdditionalInfo> EmailAdditionalInfo);

public sealed record AdditionalInfo(string Key, string Value);

Handling interim results (`State = "Unknown"`)

Some mail servers greylist first-time senders or respond slowly. Instead of failing, the API returns an interim 200 OK result with State = "Unknown", a Reason of PENDING or GREYLISTED, and a RetryAfterSeconds hint while the verification finishes in the background.

Wait RetryAfterSeconds seconds, then repeat the same request to get the final verdict.
Definitive results are cached for about 10 minutes, so the retry is answered instantly once the verification completes.
Treat Unknown as "not yet decided" — never as a delivery failure.

2

Check your credits balance

The balance endpoint is free to call and never consumes a credit — perfect for a pre-flight check before verifying a large list.

C#

var balanceResponse = await client.GetFromJsonAsync<BalanceResponse>(
    $"https://api.validemail.net/balance?token={ApiKey}");

Console.WriteLine($"Credits remaining: {balanceResponse!.Balance}");

public sealed record BalanceResponse(int Balance);

HTTP status codes

HTTP Status	Meaning	What to do
200 OK	The request was processed. Check `State` — a result with `State = "Unknown"` and a `RetryAfterSeconds` value is an interim answer, not a final verdict.	Use the result. If `State` is `Unknown`, retry the same request after `RetryAfterSeconds`.
400 Bad Request	Missing `email`/`token` parameter, no credits remaining, or a transient processing failure.	Check the response text. If you are out of credits, top up your balance before retrying.
401 Unauthorized	The API key is invalid or unknown.	Verify the `token` value against the API key shown in your dashboard.
403 Forbidden	The account attached to this API key is inactive.	Contact info@validemail.net to reactivate the account.
429 Too Many Requests	You exceeded your per-second request limit. The response body includes the configured limit.	Slow down and retry with backoff, or contact us to raise your rate limit.

Next steps

Explore every response field and status code in the full API reference.

API Reference