邮件服务是一般的系统都会拥有和需要的功能，但是对于.NET项目来说，邮件服务的创建和使用会较为的麻烦。.NET对于邮件功能提供了System.Net.Mail用于创建邮件服务，该基础服务提供邮件的基础操作，并且使用也较为的简单。对于真正将该功能使用于项目的人，就会慢慢发现其中的优缺点，甚至有些时候不能忍受其中的问题。在这里介绍一种微软用于替代System.Net.Mail的邮件服务组件MailKit和MimeKit，官网地址：http://www.mimekit.net/ 。GitHub地址：https://github.com/jstedfast/MimeKi t。下面就具体的介绍一下。
一.MailKit和MimeKit基础概述：
MailKit组件的支持的客户端类型比较多，例如SMTP客户端、POP3客户端、IMAP4客户端。该组件是一个跨平台的Email组件，该组件支持.NET 4.0，.NET 4.5，Xamarin.Android，Xamarin.iOS，Windows Phone 8.1等等平台。
MimeKit提供了一个MIME解析器，组件具备的解析特性灵活、性能高、很好的处理各种各样的破碎的MIME格式化。MimeKit的性能实际上与GMime相当。
该组件在安全性的还是比较高的，处理安全的方式较多，SASL认证、支持S / MIME v3.2、支持OpenPGP、支持DKIM签名等等方式。Mailkit组件可以通过CancellationToken取消对应的操作，CancellationToken传播应取消操作的通知，一个的CancellationToken使线程，线程池工作项目之间，或取消合作任务的对象。过实例化CancellationTokenSource对象来创建取消令牌，该对象管理从其CancellationTokenSource.Token属性检索的取消令牌。然后，将取消令牌传递到应该收到取消通知的任意数量的线程，任务或操作。令牌不能用于启动取消。
MailKit组件支持异步操作，在内部编写的有关I/O异步操作的类。
二.创建基础邮件服务：
介绍过MailKit和MimeKit组建的基础信息，接下来就介绍一下如何使用两个组件的基本功能，在这里我将基本操作做了一个简单的封装，一般的项目可以直接引用封装好的类，大家可以根据实际的情况对该组件进行扩展。
1.邮件发送基础服务API
/// <summary>
/// 邮件服务API
/// </summary>
public static class MailServiceApi
{
/// <summary>
/// 发送邮件
/// </summary>
/// <param name="mailBodyEntity">邮件基础信息</param>
/// <param name="sendServerConfiguration">发件人基础信息</param>
public static SendResultEntity SendMail(MailBodyEntity mailBodyEntity,
SendServerConfigurationEntity sendServerConfiguration)
{
if (sendServerConfiguration == null)
{
throw new ArgumentNullException();
}
if (sendServerConfiguration == null)
{
throw new ArgumentNullException();
}
var sendResultEntity = new SendResultEntity();
using (var client = new SmtpClient(new ProtocolLogger(CreateMailLog())))
{
client.ServerCertificateValidationCallback = (s, c, h, e) => true;
Connection(mailBodyEntity, sendServerConfiguration, client, sendResultEntity);
if (sendResultEntity.ResultStatus == false)
{
return sendResultEntity;
}
SmtpClientBaseMessage(client);
Authenticate(mailBodyEntity, sendServerConfiguration, client, sendResultEntity);
if (sendResultEntity.ResultStatus == false)
{
return sendResultEntity;
}
Send(mailBodyEntity, sendServerConfiguration, client, sendResultEntity);
if (sendResultEntity.ResultStatus == false)
{
return sendResultEntity;
}
client.Disconnect(true);
}
return sendResultEntity;
}
/// <summary>
/// 连接服务器
/// </summary>
/// <param name="mailBodyEntity">邮件内容</param>
/// <param name="sendServerConfiguration">发送配置</param>
/// <param name="client">客户端对象</param>
/// <param name="sendResultEntity">发送结果</param>
public static void Connection(MailBodyEntity mailBodyEntity, SendServerConfigurationEntity sendServerConfiguration,
SmtpClient client, SendResultEntity sendResultEntity)
{
try
{
client.Connect(sendServerConfiguration.SmtpHost, sendServerConfiguration.SmtpPort);
}
catch (SmtpCommandException ex)
{
sendResultEntity.ResultInformation = $"尝试连接时出错:{0}" + ex.Message;
sendResultEntity.ResultStatus = false;
}
catch (SmtpProtocolException ex)
{
sendResultEntity.ResultInformation = $"尝试连接时的协议错误:{0}" + ex.Message;
sendResultEntity.ResultStatus = false;
}
catch (Exception ex)
{
sendResultEntity.ResultInformation = $"服务器连接错误:{0}" + ex.Message;
sendResultEntity.ResultStatus = false;
}
}
/// <summary>
/// 账户认证
/// </summary>
/// <param name="mailBodyEntity">邮件内容</param>
/// <param name="sendServerConfiguration">发送配置</param>
/// <param name="client">客户端对象</param>
/// <param name="sendResultEntity">发送结果</param>
public static void Authenticate(MailBodyEntity mailBodyEntity, SendServerConfigurationEntity sendServerConfiguration,
SmtpClient client, SendResultEntity sendResultEntity)
{
try
{
client.Authenticate(sendServerConfiguration.SenderAccount, sendServerConfiguration.SenderPassword);
}
catch (AuthenticationException ex)
{
sendResultEntity.ResultInformation = $"无效的用户名或密码:{0}" + ex.Message;
sendResultEntity.ResultStatus = false;
}
catch (SmtpCommandException ex)
{
sendResultEntity.ResultInformation = $"尝试验证错误:{0}" + ex.Message;
sendResultEntity.ResultStatus = false;
}
catch (SmtpProtocolException ex)
{
sendResultEntity.ResultInformation = $"尝试验证时的协议错误:{0}" + ex.Message;
sendResultEntity.ResultStatus = false;
}
catch (Exception ex)
{
sendResultEntity.ResultInformation = $"账户认证错误:{0}" + ex.Message;
sendResultEntity.ResultStatus = false;
}
}
/// <summary>
/// 发送邮件
/// </summary>
/// <param name="mailBodyEntity">邮件内容</param>
/// <param name="sendServerConfiguration">发送配置</param>
/// <param name="client">客户端对象</param>
/// <param name="sendResultEntity">发送结果</param>
public static void Send(MailBodyEntity mailBodyEntity, SendServerConfigurationEntity sendServerConfiguration,
SmtpClient client, SendResultEntity sendResultEntity)
{
try
{
client.Send(MailMessage.AssemblyMailMessage(mailBodyEntity));
}
catch (SmtpCommandException ex)
{
switch (ex.ErrorCode)
{
case SmtpErrorCode.RecipientNotAccepted:
sendResultEntity.ResultInformation = $"收件人未被接受:{ex.Message}";
break;
case SmtpErrorCode.SenderNotAccepted:
sendResultEntity.ResultInformation = $"发件人未被接受:{ex.Message}";
break;
case SmtpErrorCode.MessageNotAccepted:
sendResultEntity.ResultInformation = $"消息未被接受:{ex.Message}";
break;
}
sendResultEntity.ResultStatus = false;
}
catch (SmtpProtocolException ex)
{
sendResultEntity.ResultInformation = $"发送消息时的协议错误:{ex.Message}";
sendResultEntity.ResultStatus = false;
}
catch (Exception ex)
{
sendResultEntity.ResultInformation = $"邮件接收失败:{ex.Message}";
sendResultEntity.ResultStatus = false;
}
}
/// <summary>
/// 获取SMTP基础信息
/// </summary>
/// <param name="client">客户端对象</param>
/// <returns></returns>
public static MailServerInformation SmtpClientBaseMessage(SmtpClient client)
{
var mailServerInformation = new MailServerInformation
{
Authentication = client.Capabilities.HasFlag(SmtpCapabilities.Authentication),
BinaryMime = client.Capabilities.HasFlag(SmtpCapabilities.BinaryMime),
Dsn = client.Capabilities.HasFlag(SmtpCapabilities.Dsn),
EightBitMime = client.Capabilities.HasFlag(SmtpCapabilities.EightBitMime),
Size = client.MaxSize
};
return mailServerInformation;
}
/// <summary>
/// 创建邮件日志文件
/// </summary>
/// <returns></returns>
public static string CreateMailLog()
{
var logPath = AppDomain.CurrentDomain.BaseDirectory + "/DocumentLog/" +
Guid.NewGuid() + ".txt";
if (File.Exists(logPath)) return logPath;
var fs = File.Create(logPath);
fs.Close();
return logPath;
}
}
2.组装邮件消息：
/// <summary>
/// 邮件信息
/// </summary>
public static class MailMessage
{
/// <summary>
/// 组装邮件文本/附件邮件信息
/// </summary>
/// <param name="mailBodyEntity">邮件消息实体</param>
/// <returns></returns>
public static MimeMessage AssemblyMailMessage(MailBodyEntity mailBodyEntity)
{
if (mailBodyEntity == null)
{
throw new ArgumentNullException(nameof(mailBodyEntity));
}
var message = new MimeMessage();
//设置邮件基本信息
SetMailBaseMessage(message, mailBodyEntity);
var multipart = new Multipart("mixed");
//插入文本消息
if (string.IsNullOrEmpty(mailBodyEntity.MailTextBody) == false)
{
var alternative = new MultipartAlternative
{
AssemblyMailTextMessage(mailBodyEntity.MailTextBody, mailBodyEntity.MailBodyType)
};
multipart.Add(alternative);
}
//插入附件
if (mailBodyEntity.MailFilePath != null && File.Exists(mailBodyEntity.MailFilePath) == false)
{
var mimePart = AssemblyMailAttachmentMessage(mailBodyEntity.MailFileType, mailBodyEntity.MailFileSubType,
mailBodyEntity.MailFilePath);
multipart.Add(mimePart);
}
//组合邮件内容
message.Body = multipart;
return message;
}
/// <summary>
/// 设置邮件基础信息
/// </summary>
/// <param name="minMessag"></param>
/// <param name="mailBodyEntity"></param>
/// <returns></returns>
public static MimeMessage SetMailBaseMessage(MimeMessage minMessag, MailBodyEntity mailBodyEntity)
{
if (minMessag == null)
{
throw new ArgumentNullException();
}
if (mailBodyEntity == null)
{
throw new ArgumentNullException();
}
//插入发件人
minMessag.From.Add(new MailboxAddress(mailBodyEntity.Sender, mailBodyEntity.SenderAddress));
//插入收件人
foreach (var recipients in mailBodyEntity.Recipients)
{
minMessag.To.Add(new MailboxAddress(recipients));
}
//插入抄送人
foreach (var cC in mailBodyEntity.Cc)
{
minMessag.Cc.Add(new MailboxAddress(cC));
}
//插入主题
minMessag.Subject = mailBodyEntity.Subject;
return minMessag;
}
/// <summary>
/// 组装邮件文本信息
/// </summary>
/// <param name="mailBody">邮件文本内容</param>
/// <param name="textPartType">邮件文本类型(plain,html,rtf,xml)</param>
/// <returns></returns>
public static TextPart AssemblyMailTextMessage(string mailBody, string textPartType)
{
if (string.IsNullOrEmpty(mailBody))
{
throw new ArgumentNullException();
}
if (string.IsNullOrEmpty(textPartType))
{
throw new ArgumentNullException();
}
var textBody = new TextPart(textPartType)
{
Text = mailBody
};
return textBody;
}
/// <summary>
/// 组装邮件附件信息
/// </summary>
/// <param name="fileAttachmentType">附件类型(image,application)</param>
/// <param name="fileAttachmentSubType">附件子类型 </param>
/// <param name="fileAttachmentPath">附件路径</param>
/// <returns></returns>
public static MimePart AssemblyMailAttachmentMessage(string fileAttachmentType, string fileAttachmentSubType, string fileAttachmentPath)
{
if (string.IsNullOrEmpty(fileAttachmentSubType))
{
throw new ArgumentNullException();
}
if (string.IsNullOrEmpty(fileAttachmentType))
{
throw new ArgumentNullException();
}
if (string.IsNullOrEmpty(fileAttachmentPath))
{
throw new ArgumentNullException();
}
var attachment = new MimePart(fileAttachmentType, fileAttachmentSubType)
{
Content = new MimeContent(File.OpenRead(fileAttachmentPath)),
ContentDisposition = new ContentDisposition(ContentDisposition.Attachment),
ContentTransferEncoding = ContentEncoding.Base64,
FileName = Path.GetFileName(fileAttachmentPath)
};
return attachment;
}
}
3.邮件基础服务实体：
/// <summary>
/// 邮件内容实体
/// </summary>
public class MailBodyEntity
{
/// <summary>
/// 邮件文本内容
/// </summary>
public string MailTextBody { get; set; }
/// <summary>
/// 邮件内容类型
/// </summary>
public string MailBodyType { get; set; }
/// <summary>
/// 邮件附件文件类型
/// </summary>
public string MailFileType { get; set; }
/// <summary>
/// 邮件附件文件子类型
/// </summary>
public string MailFileSubType { get; set; }
/// <summary>
/// 邮件附件文件路径
/// </summary>
public string MailFilePath { get; set; }
/// <summary>
/// 收件人
/// </summary>
public List<string> Recipients { get; set; }
/// <summary>
/// 抄送
/// </summary>
public List<string> Cc { get; set; }
/// <summary>
/// 发件人
/// </summary>
public string Sender { get; set; }
/// <summary>
/// 发件人地址
/// </summary>
public string SenderAddress { get; set; }
/// <summary>
/// 邮件主题
/// </summary>
public string Subject { get; set; }
/// <summary>
/// 邮件内容
/// </summary>
public string Body { get; set; }
}
/// <summary>
/// 邮件服务器基础信息
/// </summary>
public class MailServerInformation
{
/// <summary>
/// SMTP服务器支持SASL机制类型
/// </summary>
public bool Authentication { get; set; }
/// <summary>
/// SMTP服务器对消息的大小
/// </summary>
public uint Size { get; set; }
/// <summary>
/// SMTP服务器支持传递状态通知
/// </summary>
public bool Dsn { get; set; }
/// <summary>
/// SMTP服务器支持Content-Transfer-Encoding
/// </summary>
public bool EightBitMime { get; set; }
/// <summary>
/// SMTP服务器支持Content-Transfer-Encoding
/// </summary>
public bool BinaryMime { get; set; }
/// <summary>
/// SMTP服务器在消息头中支持UTF-8
/// </summary>
public string UTF8 { get; set; }
}
/// <summary>
/// 邮件发送结果
/// </summary>
public class SendResultEntity
{
/// <summary>
/// 结果信息
/// </summary>
public string ResultInformation { get; set; } = "发送成功！";
/// <summary>
/// 结果状态
/// </summary>
public bool ResultStatus { get; set; } = true;
}
/// <summary>
/// 邮件发送服务器配置
/// </summary>
public class SendServerConfigurationEntity
{
/// <summary>
/// 邮箱SMTP服务器地址
/// </summary>
public string SmtpHost { get; set; }
/// <summary>
/// 邮箱SMTP服务器端口
/// </summary>
public int SmtpPort { get; set; }
/// <summary>
/// 是否启用IsSsl
/// </summary>
public bool IsSsl { get; set; }
/// <summary>
/// 邮件编码
/// </summary>
public string MailEncoding { get; set; }
/// <summary>
/// 发件人账号
/// </summary>
public string SenderAccount { get; set; }
/// <summary>
/// 发件人密码
/// </summary>
public string SenderPassword { get; set; }
}
上面提供了借助MailKit组建创建发送邮件服务，分别是创建邮件服务器连接，组装邮件基础信息，邮件基础实体。发送邮件的基础服务比较的多，下面介绍一下邮件的接收。
/// <summary>
/// 跟投邮件服务API
/// </summary>
public static class ReceiveEmailServiceApi
{
/// <summary>
/// 设置发件人信息
/// </summary>
/// <returns></returns>
public static SendServerConfigurationEntity SetSendMessage()
{
var sendServerConfiguration = new SendServerConfigurationEntity
{
SmtpHost = ConfigurationManager.AppSettings["SmtpServer"],
SmtpPort = int.Parse(ConfigurationManager.AppSettings["SmtpPort"]),
IsSsl = Convert.ToBoolean(ConfigurationManager.AppSettings["IsSsl"]),
MailEncoding = ConfigurationManager.AppSettings["MailEncoding"],
SenderAccount = ConfigurationManager.AppSettings["SenderAccount"],
SenderPassword = ConfigurationManager.AppSettings["SenderPassword"]
};
return sendServerConfiguration;
}
/// <summary>
/// 接收邮件
/// </summary>
public static void ReceiveEmail()
{
var sendServerConfiguration = SetSendMessage();
if (sendServerConfiguration == null)
{
throw new ArgumentNullException();
}
using (var client = new ImapClient(new ProtocolLogger(CreateMailLog())))
{
client.Connect(sendServerConfiguration.SmtpHost, sendServerConfiguration.SmtpPort,
SecureSocketOptions.SslOnConnect);
client.Authenticate(sendServerConfiguration.SenderAccount, sendServerConfiguration.SenderPassword);
client.Inbox.Open(FolderAccess.ReadOnly);
var uids = client.Inbox.Search(SearchQuery.All);
foreach (var uid in uids)
{
var message = client.Inbox.GetMessage(uid);
message.WriteTo($"{uid}.eml");
}
client.Disconnect(true);
}
}
/// <summary>
/// 下载邮件内容
/// </summary>
public static void DownloadBodyParts()
{
var sendServerConfiguration = SetSendMessage();
using (var client = new ImapClient())
{
client.Connect(sendServerConfiguration.SmtpHost, sendServerConfiguration.SmtpPort,
SecureSocketOptions.SslOnConnect);
client.Authenticate(sendServerConfiguration.SenderAccount, sendServerConfiguration.SenderPassword);
client.Inbox.Open(FolderAccess.ReadOnly);
// 搜索Subject标题包含“MimeKit”或“MailKit”的邮件
var query = SearchQuery.SubjectContains("MimeKit").Or(SearchQuery.SubjectContains("MailKit"));
var uids = client.Inbox.Search(query);
// 获取搜索结果的摘要信息（我们需要UID和BODYSTRUCTURE每条消息，以便我们可以提取文本正文和附件）
var items = client.Inbox.Fetch(uids, MessageSummaryItems.UniqueId | MessageSummaryItems.BodyStructure);
foreach (var item in items)
{
// 确定一个目录来保存内容
var directory = Path.Combine(AppDomain.CurrentDomain.BaseDirectory + "/MailBody", item.UniqueId.ToString());
Directory.CreateDirectory(directory);
// IMessageSummary.TextBody是一个便利的属性，可以为我们找到“文本/纯文本”的正文部分
var bodyPart = item.TextBody;
// 下载'text / plain'正文部分
var body = (TextPart) client.Inbox.GetBodyPart(item.UniqueId, bodyPart);
// TextPart.Text是一个便利的属性，它解码内容并将结果转换为我们的字符串
var text = body.Text;
File.WriteAllText(Path.Combine(directory, "body.txt"), text);
// 现在遍历所有附件并将其保存到磁盘
foreach (var attachment in item.Attachments)
{
// 像我们对内容所做的那样下载附件
var entity = client.Inbox.GetBodyPart(item.UniqueId, attachment);
// 附件可以是message / rfc822部件或常规MIME部件
var messagePart = entity as MessagePart;
if (messagePart != null)
{
var rfc822 = messagePart;
var path = Path.Combine(directory, attachment.PartSpecifier + ".eml");
rfc822.Message.WriteTo(path);
}
else
{
var part = (MimePart) entity;
// 注意：这可能是空的，但大多数会指定一个文件名
var fileName = part.FileName;
var path = Path.Combine(directory, fileName);
// decode and save the content to a file
using (var stream = File.Create(path))
part.Content.DecodeTo(stream);
}
}
}
client.Disconnect(true);
}
}
/// <summary>
/// 创建邮件日志文件
/// </summary>
/// <returns></returns>
public static string CreateMailLog()
{
var logPath = AppDomain.CurrentDomain.BaseDirectory + "/DocumentLog/" +
DateTime.Now.ToUniversalTime().ToString(CultureInfo.InvariantCulture) + ".txt";
if (File.Exists(logPath)) return logPath;
var fs = File.Create(logPath);
fs.Close();
return logPath;
}
}
面只是简单的介绍了邮件的接收，如果需要更加深入的了解功能，可以进一步对组件源码进行解析，该组件的文档为较为的丰富。
三.组件使用感悟：
MailKit和MimeKit组件在项目的使用中较为的便捷，基本包含了所有的基础邮件服务操作。组件提供的SmtpClient类提供的功能很丰富，例如连接邮件服务器，邮件账户认证，组装邮件消息，获取邮件服务器配置信息等等方法的提供，可以让我们在项目中快速的获取邮件服务的所有信息。
使用过邮件功能的项目 都会有困扰，客户端与邮件服务器的连接是否成功，以及邮件是否发送成功状态没有办法很快的获取，只能根据邮件服务器返回的一场状态进行判断。但是MailKit提供对应的方法和异常类，对邮件服务器返回的异常信息进行解析，客户端可以根据这些异常类获取邮件状态。
MailKit组件的提供了ProtocolLogger类，该类用于记录SMTP操作基础信息，该类作用为记录邮件服务日志。在邮件发送完毕后，需要及时的关闭连接，调用Disconnect(true)方法。