mailpit-integration

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English

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Email Testing with Mailpit and .NET Aspire

结合Mailpit与.NET Aspire进行邮件测试

When to Use This Skill

何时使用此技能

Use this skill when:

Testing email delivery locally without sending real emails
Setting up email infrastructure in .NET Aspire
Writing integration tests that verify emails are sent
Debugging email rendering and headers

Related skills:

```
aspnetcore/mjml-email-templates
```
- MJML template authoring
```
testing/verify-email-snapshots
```
- Snapshot test rendered HTML
```
aspire/integration-testing
```
- General Aspire testing patterns

在以下场景使用此技能：

在本地测试邮件投递，无需发送真实邮件
在.NET Aspire中搭建邮件基础设施
编写验证邮件发送情况的集成测试
调试邮件渲染效果与邮件头

相关技能：

```
aspnetcore/mjml-email-templates
```
- MJML模板编写
```
testing/verify-email-snapshots
```
- 快照测试渲染后的HTML
```
aspire/integration-testing
```
- Aspire通用测试模式

What is Mailpit?

什么是Mailpit？

Mailpit is a lightweight email testing tool that:

Captures all SMTP traffic without delivering emails
Provides a web UI to view captured emails
Exposes an API for programmatic access
Supports HTML rendering, headers, and attachments

Perfect for development and integration testing.

Mailpit是一款轻量级邮件测试工具，具备以下功能：

捕获所有SMTP流量，不实际投递邮件
提供Web UI查看捕获的邮件
暴露API支持程序化访问
支持HTML渲染、邮件头与附件查看

非常适合开发与集成测试场景。

Aspire AppHost Configuration

Aspire AppHost配置

Add Mailpit as a container in your AppHost:

csharp

// AppHost/Program.cs
var builder = DistributedApplication.CreateBuilder(args);

// Add Mailpit for email testing
var mailpit = builder.AddContainer("mailpit", "axllent/mailpit")
    .WithHttpEndpoint(port: 8025, targetPort: 8025, name: "ui")
    .WithEndpoint(port: 1025, targetPort: 1025, name: "smtp");

// Reference in your API project
var api = builder.AddProject<Projects.MyApp_Api>("api")
    .WithReference(mailpit.GetEndpoint("smtp"))
    .WithEnvironment("Smtp__Host", mailpit.GetEndpoint("smtp"));

builder.Build().Run();

在你的AppHost中添加Mailpit容器：

csharp

// AppHost/Program.cs
var builder = DistributedApplication.CreateBuilder(args);

// 添加Mailpit用于邮件测试
var mailpit = builder.AddContainer("mailpit", "axllent/mailpit")
    .WithHttpEndpoint(port: 8025, targetPort: 8025, name: "ui")
    .WithEndpoint(port: 1025, targetPort: 1025, name: "smtp");

// 在API项目中引用
var api = builder.AddProject<Projects.MyApp_Api>("api")
    .WithReference(mailpit.GetEndpoint("smtp"))
    .WithEnvironment("Smtp__Host", mailpit.GetEndpoint("smtp"));

builder.Build().Run();

SMTP Configuration

SMTP配置

appsettings.json

json

{
  "Smtp": {
    "Host": "localhost",
    "Port": 1025,
    "EnableSsl": false,
    "FromAddress": "noreply@myapp.com",
    "FromName": "MyApp"
  }
}

json

{
  "Smtp": {
    "Host": "localhost",
    "Port": 1025,
    "EnableSsl": false,
    "FromAddress": "noreply@myapp.com",
    "FromName": "MyApp"
  }
}

Configuration Class

配置类

csharp

public class SmtpSettings
{
    public string Host { get; set; } = "localhost";
    public int Port { get; set; } = 1025;
    public bool EnableSsl { get; set; } = false;
    public string FromAddress { get; set; } = "noreply@myapp.com";
    public string FromName { get; set; } = "MyApp";

    // Optional: For production SMTP
    public string? Username { get; set; }
    public string? Password { get; set; }
}

csharp

public class SmtpSettings
{
    public string Host { get; set; } = "localhost";
    public int Port { get; set; } = 1025;
    public bool EnableSsl { get; set; } = false;
    public string FromAddress { get; set; } = "noreply@myapp.com";
    public string FromName { get; set; } = "MyApp";

    // 可选：生产环境SMTP配置
    public string? Username { get; set; }
    public string? Password { get; set; }
}

Service Registration

服务注册

csharp

// In Program.cs or extension method
services.Configure<SmtpSettings>(configuration.GetSection("Smtp"));

services.AddSingleton<IEmailSender>(sp =>
{
    var settings = sp.GetRequiredService<IOptions<SmtpSettings>>().Value;
    return new SmtpEmailSender(settings);
});

csharp

// 在Program.cs或扩展方法中
services.Configure<SmtpSettings>(configuration.GetSection("Smtp"));

services.AddSingleton<IEmailSender>(sp =>
{
    var settings = sp.GetRequiredService<IOptions<SmtpSettings>>().Value;
    return new SmtpEmailSender(settings);
});

Email Sender Implementation

邮件发送器实现

csharp

public interface IEmailSender
{
    Task SendEmailAsync(EmailMessage message, CancellationToken ct = default);
}

public sealed class SmtpEmailSender : IEmailSender
{
    private readonly SmtpSettings _settings;

    public SmtpEmailSender(SmtpSettings settings)
    {
        _settings = settings;
    }

    public async Task SendEmailAsync(EmailMessage message, CancellationToken ct = default)
    {
        using var client = new SmtpClient();

        await client.ConnectAsync(
            _settings.Host,
            _settings.Port,
            _settings.EnableSsl ? SecureSocketOptions.StartTls : SecureSocketOptions.None,
            ct);

        if (!string.IsNullOrEmpty(_settings.Username))
        {
            await client.AuthenticateAsync(_settings.Username, _settings.Password, ct);
        }

        var mailMessage = new MimeMessage();
        mailMessage.From.Add(new MailboxAddress(_settings.FromName, _settings.FromAddress));
        mailMessage.To.Add(new MailboxAddress(message.ToName, message.To));
        mailMessage.Subject = message.Subject;

        var bodyBuilder = new BodyBuilder { HtmlBody = message.HtmlBody };
        mailMessage.Body = bodyBuilder.ToMessageBody();

        await client.SendAsync(mailMessage, ct);
        await client.DisconnectAsync(true, ct);
    }
}

Requires

MailKit

package:

bash

dotnet add package MailKit

csharp

public interface IEmailSender
{
    Task SendEmailAsync(EmailMessage message, CancellationToken ct = default);
}

public sealed class SmtpEmailSender : IEmailSender
{
    private readonly SmtpSettings _settings;

    public SmtpEmailSender(SmtpSettings settings)
    {
        _settings = settings;
    }

    public async Task SendEmailAsync(EmailMessage message, CancellationToken ct = default)
    {
        using var client = new SmtpClient();

        await client.ConnectAsync(
            _settings.Host,
            _settings.Port,
            _settings.EnableSsl ? SecureSocketOptions.StartTls : SecureSocketOptions.None,
            ct);

        if (!string.IsNullOrEmpty(_settings.Username))
        {
            await client.AuthenticateAsync(_settings.Username, _settings.Password, ct);
        }

        var mailMessage = new MimeMessage();
        mailMessage.From.Add(new MailboxAddress(_settings.FromName, _settings.FromAddress));
        mailMessage.To.Add(new MailboxAddress(message.ToName, message.To));
        mailMessage.Subject = message.Subject;

        var bodyBuilder = new BodyBuilder { HtmlBody = message.HtmlBody };
        mailMessage.Body = bodyBuilder.ToMessageBody();

        await client.SendAsync(mailMessage, ct);
        await client.DisconnectAsync(true, ct);
    }
}

需要安装

MailKit

包：

bash

dotnet add package MailKit

Viewing Captured Emails

查看捕获的邮件

Web UI

Navigate to

http://localhost:8025

to see:

Inbox - All captured emails
HTML view - Rendered email
Source view - Raw HTML/MJML output
Headers - Full email headers
Attachments - Any attached files

访问

http://localhost:8025

即可查看：

收件箱 - 所有捕获的邮件
HTML视图 - 渲染后的邮件内容
源码视图 - 原始HTML/MJML输出
邮件头 - 完整的邮件头信息
附件 - 所有附加文件

Aspire Dashboard

Aspire仪表板

The Mailpit UI endpoint appears in the Aspire dashboard under Resources.

Mailpit的UI端点会显示在Aspire仪表板的资源列表中。

Integration Testing

集成测试

Test Fixture with Aspire

基于Aspire的测试夹具

csharp

public class EmailIntegrationTests : IClassFixture<AspireFixture>
{
    private readonly HttpClient _client;
    private readonly MailpitClient _mailpit;

    public EmailIntegrationTests(AspireFixture fixture)
    {
        _client = fixture.CreateClient();
        _mailpit = new MailpitClient(fixture.GetMailpitUrl());
    }

    [Fact]
    public async Task SignupFlow_SendsWelcomeEmail()
    {
        // Arrange
        await _mailpit.ClearMessagesAsync();

        // Act - Trigger signup flow
        var response = await _client.PostAsJsonAsync("/api/auth/signup", new
        {
            Email = "test@example.com",
            Password = "SecurePassword123!"
        });
        response.EnsureSuccessStatusCode();

        // Assert - Verify email was sent
        var messages = await _mailpit.GetMessagesAsync();

        var welcomeEmail = messages.Should().ContainSingle()
            .Which;

        welcomeEmail.To.Should().Contain("test@example.com");
        welcomeEmail.Subject.Should().Contain("Welcome");
        welcomeEmail.HtmlBody.Should().Contain("Thank you for signing up");
    }
}

csharp

public class EmailIntegrationTests : IClassFixture<AspireFixture>
{
    private readonly HttpClient _client;
    private readonly MailpitClient _mailpit;

    public EmailIntegrationTests(AspireFixture fixture)
    {
        _client = fixture.CreateClient();
        _mailpit = new MailpitClient(fixture.GetMailpitUrl());
    }

    [Fact]
    public async Task SignupFlow_SendsWelcomeEmail()
    {
        // 准备
        await _mailpit.ClearMessagesAsync();

        // 执行 - 触发注册流程
        var response = await _client.PostAsJsonAsync("/api/auth/signup", new
        {
            Email = "test@example.com",
            Password = "SecurePassword123!"
        });
        response.EnsureSuccessStatusCode();

        // 断言 - 验证邮件已发送
        var messages = await _mailpit.GetMessagesAsync();

        var welcomeEmail = messages.Should().ContainSingle()
            .Which;

        welcomeEmail.To.Should().Contain("test@example.com");
        welcomeEmail.Subject.Should().Contain("Welcome");
        welcomeEmail.HtmlBody.Should().Contain("Thank you for signing up");
    }
}

Mailpit API Client

Mailpit API客户端

csharp

public class MailpitClient
{
    private readonly HttpClient _client;

    public MailpitClient(string baseUrl)
    {
        _client = new HttpClient { BaseAddress = new Uri(baseUrl) };
    }

    public async Task<List<MailpitMessage>> GetMessagesAsync()
    {
        var response = await _client.GetFromJsonAsync<MailpitResponse>("/api/v1/messages");
        return response?.Messages ?? new List<MailpitMessage>();
    }

    public async Task ClearMessagesAsync()
    {
        await _client.DeleteAsync("/api/v1/messages");
    }

    public async Task<MailpitMessage?> WaitForMessageAsync(
        Func<MailpitMessage, bool> predicate,
        TimeSpan timeout)
    {
        var deadline = DateTime.UtcNow + timeout;

        while (DateTime.UtcNow < deadline)
        {
            var messages = await GetMessagesAsync();
            var match = messages.FirstOrDefault(predicate);

            if (match != null)
                return match;

            await Task.Delay(100);
        }

        return null;
    }
}

public class MailpitResponse
{
    public List<MailpitMessage> Messages { get; set; } = new();
}

public class MailpitMessage
{
    public string Id { get; set; } = "";
    public List<string> To { get; set; } = new();
    public string Subject { get; set; } = "";
    public string HtmlBody { get; set; } = "";
}

csharp

public class MailpitClient
{
    private readonly HttpClient _client;

    public MailpitClient(string baseUrl)
    {
        _client = new HttpClient { BaseAddress = new Uri(baseUrl) };
    }

    public async Task<List<MailpitMessage>> GetMessagesAsync()
    {
        var response = await _client.GetFromJsonAsync<MailpitResponse>("/api/v1/messages");
        return response?.Messages ?? new List<MailpitMessage>();
    }

    public async Task ClearMessagesAsync()
    {
        await _client.DeleteAsync("/api/v1/messages");
    }

    public async Task<MailpitMessage?> WaitForMessageAsync(
        Func<MailpitMessage, bool> predicate,
        TimeSpan timeout)
    {
        var deadline = DateTime.UtcNow + timeout;

        while (DateTime.UtcNow < deadline)
        {
            var messages = await GetMessagesAsync();
            var match = messages.FirstOrDefault(predicate);

            if (match != null)
                return match;

            await Task.Delay(100);
        }

        return null;
    }
}

public class MailpitResponse
{
    public List<MailpitMessage> Messages { get; set; } = new();
}

public class MailpitMessage
{
    public string Id { get; set; } = "";
    public List<string> To { get; set; } = new();
    public string Subject { get; set; } = "";
    public string HtmlBody { get; set; } = "";
}

Aspire Test Fixture

Aspire测试夹具

csharp

public class AspireFixture : IAsyncLifetime
{
    private DistributedApplication? _app;
    private string _mailpitUrl = "";

    public async Task InitializeAsync()
    {
        var appHost = await DistributedApplicationTestingBuilder
            .CreateAsync<Projects.MyApp_AppHost>();

        // Disable persistence for clean tests
        appHost.Configuration["MyApp:UseVolumes"] = "false";

        _app = await appHost.BuildAsync();
        await _app.StartAsync();

        // Get Mailpit URL from Aspire
        var mailpit = _app.GetContainerResource("mailpit");
        _mailpitUrl = await mailpit.GetEndpointAsync("ui");
    }

    public HttpClient CreateClient()
    {
        var api = _app!.GetProjectResource("api");
        return api.CreateHttpClient();
    }

    public string GetMailpitUrl() => _mailpitUrl;

    public async Task DisposeAsync()
    {
        if (_app != null)
            await _app.DisposeAsync();
    }
}

csharp

public class AspireFixture : IAsyncLifetime
{
    private DistributedApplication? _app;
    private string _mailpitUrl = "";

    public async Task InitializeAsync()
    {
        var appHost = await DistributedApplicationTestingBuilder
            .CreateAsync<Projects.MyApp_AppHost>();

        // 禁用持久化以保证测试环境干净
        appHost.Configuration["MyApp:UseVolumes"] = "false";

        _app = await appHost.BuildAsync();
        await _app.StartAsync();

        // 从Aspire获取Mailpit的URL
        var mailpit = _app.GetContainerResource("mailpit");
        _mailpitUrl = await mailpit.GetEndpointAsync("ui");
    }

    public HttpClient CreateClient()
    {
        var api = _app!.GetProjectResource("api");
        return api.CreateHttpClient();
    }

    public string GetMailpitUrl() => _mailpitUrl;

    public async Task DisposeAsync()
    {
        if (_app != null)
            await _app.DisposeAsync();
    }
}

Common Test Patterns

常见测试模式

Wait for Async Email

等待异步邮件

Some emails are sent asynchronously. Wait for them:

csharp

[Fact]
public async Task AsyncWorkflow_EventuallySendsEmail()
{
    await _mailpit.ClearMessagesAsync();

    // Trigger async workflow
    await _client.PostAsync("/api/workflows/start", null);

    // Wait for email (with timeout)
    var email = await _mailpit.WaitForMessageAsync(
        m => m.Subject.Contains("Workflow Complete"),
        timeout: TimeSpan.FromSeconds(10));

    email.Should().NotBeNull();
}

部分邮件是异步发送的，需等待其生成：

csharp

[Fact]
public async Task AsyncWorkflow_EventuallySendsEmail()
{
    await _mailpit.ClearMessagesAsync();

    // 触发异步工作流
    await _client.PostAsync("/api/workflows/start", null);

    // 等待邮件（带超时）
    var email = await _mailpit.WaitForMessageAsync(
        m => m.Subject.Contains("Workflow Complete"),
        timeout: TimeSpan.FromSeconds(10));

    email.Should().NotBeNull();
}

Verify Multiple Emails

验证多封邮件

csharp

[Fact]
public async Task BulkOperation_SendsMultipleEmails()
{
    await _mailpit.ClearMessagesAsync();

    await _client.PostAsJsonAsync("/api/invitations/bulk", new
    {
        Emails = new[] { "a@test.com", "b@test.com", "c@test.com" }
    });

    var messages = await _mailpit.WaitForMessagesAsync(
        expectedCount: 3,
        timeout: TimeSpan.FromSeconds(10));

    messages.Should().HaveCount(3);
    messages.Select(m => m.To.First())
        .Should().BeEquivalentTo("a@test.com", "b@test.com", "c@test.com");
}

csharp

[Fact]
public async Task BulkOperation_SendsMultipleEmails()
{
    await _mailpit.ClearMessagesAsync();

    await _client.PostAsJsonAsync("/api/invitations/bulk", new
    {
        Emails = new[] { "a@test.com", "b@test.com", "c@test.com" }
    });

    var messages = await _mailpit.WaitForMessagesAsync(
        expectedCount: 3,
        timeout: TimeSpan.FromSeconds(10));

    messages.Should().HaveCount(3);
    messages.Select(m => m.To.First())
        .Should().BeEquivalentTo("a@test.com", "b@test.com", "c@test.com");
}

Verify Email Content

验证邮件内容

csharp

[Fact]
public async Task PasswordReset_ContainsValidResetLink()
{
    await _mailpit.ClearMessagesAsync();

    await _client.PostAsJsonAsync("/api/auth/forgot-password", new
    {
        Email = "user@test.com"
    });

    var email = await _mailpit.WaitForMessageAsync(
        m => m.Subject.Contains("Password Reset"),
        timeout: TimeSpan.FromSeconds(5));

    // Extract reset link from HTML
    var resetLink = Regex.Match(email!.HtmlBody, @"href=""([^""]+/reset/[^""]+)""")
        .Groups[1].Value;

    resetLink.Should().StartWith("https://myapp.com/reset/");

    // Verify the link works
    var resetResponse = await _client.GetAsync(resetLink);
    resetResponse.StatusCode.Should().Be(HttpStatusCode.OK);
}

csharp

[Fact]
public async Task PasswordReset_ContainsValidResetLink()
{
    await _mailpit.ClearMessagesAsync();

    await _client.PostAsJsonAsync("/api/auth/forgot-password", new
    {
        Email = "user@test.com"
    });

    var email = await _mailpit.WaitForMessageAsync(
        m => m.Subject.Contains("Password Reset"),
        timeout: TimeSpan.FromSeconds(5));

    // 从HTML中提取重置链接
    var resetLink = Regex.Match(email!.HtmlBody, @"href=""([^""]+/reset/[^""]+)""")
        .Groups[1].Value;

    resetLink.Should().StartWith("https://myapp.com/reset/");

    // 验证链接有效性
    var resetResponse = await _client.GetAsync(resetLink);
    resetResponse.StatusCode.Should().Be(HttpStatusCode.OK);
}

Production vs Development

生产环境与开发环境对比

csharp

services.AddSingleton<IEmailSender>(sp =>
{
    var settings = sp.GetRequiredService<IOptions<SmtpSettings>>().Value;
    var env = sp.GetRequiredService<IHostEnvironment>();

    if (env.IsDevelopment())
    {
        // Mailpit - no auth, no SSL
        return new SmtpEmailSender(settings);
    }
    else
    {
        // Production SMTP (SendGrid, Postmark, etc.)
        return new SmtpEmailSender(settings with
        {
            EnableSsl = true
        });
    }
});

csharp

services.AddSingleton<IEmailSender>(sp =>
{
    var settings = sp.GetRequiredService<IOptions<SmtpSettings>>().Value;
    var env = sp.GetRequiredService<IHostEnvironment>();

    if (env.IsDevelopment())
    {
        // 开发环境使用Mailpit - 无需认证、无需SSL
        return new SmtpEmailSender(settings);
    }
    else
    {
        // 生产环境SMTP（如SendGrid、Postmark等）
        return new SmtpEmailSender(settings with
        {
            EnableSsl = true
        });
    }
});

Troubleshooting

故障排查

Emails Not Appearing

邮件未显示

Check Mailpit container is running in Aspire dashboard
Verify SMTP host/port configuration
Check for exceptions in application logs

检查Aspire仪表板中Mailpit容器是否正在运行
验证SMTP主机/端口配置是否正确
查看应用程序日志中的异常信息

Connection Refused

连接被拒绝

bash

undefined

bash

undefined

Verify Mailpit is listening

验证Mailpit是否在监听

curl http://localhost:8025/api/v1/messages

undefined

curl http://localhost:8025/api/v1/messages

undefined

Aspire Endpoint Not Resolving

Aspire端点无法解析

csharp

// Ensure endpoint reference is correct
.WithEnvironment("Smtp__Host", mailpit.GetEndpoint("smtp").Property(EndpointProperty.Host))
.WithEnvironment("Smtp__Port", mailpit.GetEndpoint("smtp").Property(EndpointProperty.Port))

csharp

// 确保端点引用正确
.WithEnvironment("Smtp__Host", mailpit.GetEndpoint("smtp").Property(EndpointProperty.Host))
.WithEnvironment("Smtp__Port", mailpit.GetEndpoint("smtp").Property(EndpointProperty.Port))

Resources

资源

Mailpit: https://github.com/axllent/mailpit
Mailpit API: https://mailpit.axllent.org/docs/api-v1/
MailKit: https://github.com/jstedfast/MailKit
Aspire Containers: https://learn.microsoft.com/en-us/dotnet/aspire/fundamentals/container-resources

Mailpit: https://github.com/axllent/mailpit
Mailpit API: https://mailpit.axllent.org/docs/api-v1/
MailKit: https://github.com/jstedfast/MailKit
Aspire容器: https://learn.microsoft.com/en-us/dotnet/aspire/fundamentals/container-resources