Tutorials

Email Testing in C# and .NET

The Devmailr TeamJune 23, 20266 min read

.NET apps send verification and reset emails like any other — and your xUnit (or NUnit) suite can confirm they actually go out by reading them from a disposable inbox. Here’s a small HttpClient-based client and a test.

A small client (HttpClient)

Devmailr.cs

using System.Net.Http.Json;
using System.Text.Json;

public class Devmailr
{
    private readonly HttpClient _http = new()
    {
        BaseAddress = new Uri("https://api.devmailr.app/api/"),
        Timeout = TimeSpan.FromSeconds(65), // /wait long-polls
    };

    public Devmailr()
    {
        var key = Environment.GetEnvironmentVariable("DEVMAILR_API_KEY");
        _http.DefaultRequestHeaders.Authorization = new("Bearer", key);
    }

    public async Task<JsonElement> CreateInboxAsync(string prefix)
    {
        var res = await _http.PostAsJsonAsync("mailboxes", new { prefix });
        return await res.Content.ReadFromJsonAsync<JsonElement>();
    }

    public async Task<JsonElement> WaitForEmailAsync(string id, string query = "")
    {
        var res = await _http.GetAsync($"mailboxes/{id}/wait?timeout=60&{query}");
        return await res.Content.ReadFromJsonAsync<JsonElement>();
    }

    public Task DeleteInboxAsync(string id) => _http.DeleteAsync($"mailboxes/{id}");
}

The test (xUnit)

SignupEmailTests.cs

using Xunit;

public class SignupEmailTests
{
    [Fact]
    public async Task Signup_Sends_Verification_Code()
    {
        var dm = new Devmailr();
        var inbox = await dm.CreateInboxAsync($"net-{DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()}");
        var address = inbox.GetProperty("address").GetString();
        var id = inbox.GetProperty("_id").GetString()!;

        // trigger your app to email a code to 'address'
        await SignUpAsync(address);

        var email = await dm.WaitForEmailAsync(id, "has_code=true");
        var code = email.GetProperty("extractedCodes")[0].GetString();

        Assert.Matches(@"^\d{6}$", code);

        await dm.DeleteInboxAsync(id);
    }
}

Magic links and reset links

csharp

var email = await dm.WaitForEmailAsync(id, "subject=" + Uri.EscapeDataString("reset"));
var link = email.GetProperty("primaryLink").GetString();

Tips

Keep HttpClient.Timeout above the wait timeout (65s above; the default 100s also covers it).
Set DEVMAILR_API_KEY as a CI secret / environment variable.
NUnit works the same — swap [Fact] for [Test].
Unique prefix per test (a Unix-ms timestamp) for parallel safety.