使用 SmtpClient 发送邮件时图像中断答案

【问题标题】：Images breaking when sending mail using SmtpClient使用 SmtpClient 发送邮件时图像中断
【发布时间】：2013-05-20 04:48:21
【问题描述】：

我正在使用 C# 使用 SmtpClient 类发送邮件。在发送邮件之前，我正在做以下事情。

var mailMessage = new MailMessage();

model.ToAddresses.ForEach(to => mailMessage.To.Add(to));
mailMessage.Subject = "Test Email - By Yasser";

mailMessage.Body = String.Format("{0}{1}{2}",
                                    "<html><body>",
                                     GetEmailContent(model),
                                     "</body></html>");
mailMessage.IsBodyHtml = true;
return MailService.SendEmail(mailMessage);

下面是我的 MailService 类：

public class MailService
{
    public static bool SendEmail(MailMessage mailMessage)
    {
        var smtpClient = new SmtpClient();
        try
        {
            smtpClient.Send(mailMessage);
            return true;
        }
        catch(Exception exp)
        {
            return false;
        }
    }
}

现在当我发送邮件时，邮件被发送，这是我在按查看源时在 Outlook 中得到的邮件内容。下面是邮件的内容，有图源（显然我只保留了部分图片数据）

<html>

<body>
    <h1>Test</h1>
    <h2>Hello World</h2>
    <h3>Missing close h3 tag</h3>

    <p>
        <a href="www.google.com">
            <img src="data:image/gif;base64,/9j/4AAQSkZJRgABAgEAYABgAAD/4Q8HRXhpZgAAT" />
        </a>
    </p>
</body>

</html>

所以这在邮件中显示为损坏（图像），但是当我复制此源并将其粘贴到编辑器并使用浏览器打开文件时，一切似乎都很好（甚至图像）。

更新：添加了来自 Outlook 的邮件图片

有什么想法吗？？？？

【问题讨论】：

澄清一下：您的问题是，图像没有在电子邮件中加载（显示）？是否显示无法加载图像的图标？
您可能想试试邮件在 gmail 或其他网络邮件程序中的外观。验证问题是否存在于所有邮件客户端，而不仅仅是 Outlook。
如何将图像添加到电子邮件中？您是否正在使用自己的方法来获取嵌入图像所需的字符串或诸如AlternateView 之类的内置内容？
你可能想看看这个问题的答案：stackoverflow.com/questions/9110091/…
@Anubis1233 在 Thunderbird 和 gmail 中试过，看起来一样...

标签： c# html email smtpclient

【解决方案1】：

这是我尝试并为我工作的方法，在 Outlook、Thunderbird 和 gmail 中进行了测试。工作正常！

您可能想查看我提到的以下资源：

示例代码：

// we need to use the prefix 'cid' in the img src value
string emailReadyHtml = string.empty;
emailReadyHtml += "<p>Hello World, below are two embedded images : </p>";
emailReadyHtml += "<img src=\"cid:yasser\" >";
emailReadyHtml += "<img src=\"cid:smile\" >";

MailMessage mailMessage = new MailMessage();

mailMessage.To.Add("yasser@mail.yy");
mailMessage.From = new MailAddress("info@mail.yy", "Info");

mailMessage.Subject = "Test Mail";
mailMessage.IsBodyHtml = true;

string image1Path = HttpContext.Current.Server.MapPath("~/Content/images/yasser.jpg");
byte[] image2Bytes = someArrayOfByte;

ContentType c = new ContentType("image/jpeg");

// create image resource from image path using LinkedResource class.
LinkedResource linkedResource1 = new LinkedResource(imagePath);
linkedResource1.ContentType = c ;
linkedResource1.ContentId = "yasser";
linkedResource1.TransferEncoding = TransferEncoding.Base64;

// the linked resource can be created from bytes also, which may be stored in database (which was my case)
LinkedResource linkedResource2 = new LinkedResource(new MemoryStream(image2Bytes));
linkedResource2.ContentType = c;
linkedResource2.ContentId = "smile";
linkedResource2.TransferEncoding = TransferEncoding.Base64;

AlternateView alternativeView = AlternateView.CreateAlternateViewFromString(emailReadyHtml, null, MediaTypeNames.Text.Html);

alternativeView.ContentId = "htmlView";
alternativeView.TransferEncoding = TransferEncoding.SevenBit;

alternativeView.LinkedResources.Add(linkedResource1) ;
alternativeView.LinkedResources.Add(linkedResource2);

mailMessage.AlternateViews.Add(alternativeView);

SmtpClient smtpClient = new SmtpClient();
smtpClient.Send(mailMessage);

【讨论】：

您永远不会将正文分配给 mailMessage。此代码不起作用。
您是否尝试过代码@AAlferez？最好分配一个主体，但这不是必需的。

【解决方案2】：

这是一个可以解决问题的函数。在发送电子邮件之前调用它，例如：

ProcessEmbeddingImages(mailMessage);
return MailService.SendEmail(mailMessage);

ProcessEmbeddingImages 函数是用 VB.Net 编写的，因此您可能希望使用其中一种在线翻译器将其翻译成 c#。

Private Sub ProcessEmbeddingImages(ByRef oMail As System.Net.Mail.MailMessage)
    Dim oLinkedResources As New Hashtable()
    oMail.Body = PadSrcDataImage(oMail.Body, oLinkedResources)
    If oLinkedResources.Count > 0 Then

        Dim oAlternateView As System.Net.Mail.AlternateView = System.Net.Mail.AlternateView.CreateAlternateViewFromString(oMail.Body, Nothing, "text/html")
        oAlternateView.ContentId = "htmlView"
        oAlternateView.TransferEncoding = Net.Mime.TransferEncoding.SevenBit

        For Each oItem As DictionaryEntry In oLinkedResources
            Dim oKey As String() = Split(oItem.Key, "-")
            Dim i As Integer = oKey(0)
            Dim sExt As String = oKey(1)
            Dim sData As String = oItem.Value

            Dim oLinkedResource As New System.Net.Mail.LinkedResource(New IO.MemoryStream(System.Convert.FromBase64String(sData)))
            oLinkedResource.ContentId = "MyImg" & i
            oLinkedResource.TransferEncoding = Net.Mime.TransferEncoding.Base64
            oLinkedResource.ContentType = New System.Net.Mime.ContentType("image/" & sExt)
            oAlternateView.LinkedResources.Add(oLinkedResource)
        Next

        oMail.AlternateViews.Add(oAlternateView)
    End If
End Sub

Private Function PadSrcDataImage(ByVal sHtml As String, ByRef oLinkedResources As Hashtable) As String

    Dim oList As New ArrayList
    Dim sSearch As String = "\ssrc=['""]data:image/(.*?);base64,(.*?)['""]"

    Dim oMatches As System.Text.RegularExpressions.MatchCollection = System.Text.RegularExpressions.Regex.Matches(sHtml, sSearch, System.Text.RegularExpressions.RegexOptions.IgnoreCase)
    For Each m As System.Text.RegularExpressions.Match In oMatches
        If m.Groups.Count >= 2 Then
            Dim sExt As String = m.Groups(1).Value
            Dim sData As String = m.Groups(2).Value

            If sData.Length > 7 AndAlso Right(sData, 6) = "%3D%3D" Then
                'Replace trailing %3D%3D with ==
                sData = Left(sData, sData.Length - 6) & "=="
            End If

            oLinkedResources.Add(oLinkedResources.Count & "-" & sExt, sData)

            Dim iPos1 As Integer = m.Groups(1).Index - "data:image/".Length
            Dim iPos2 As Integer = m.Groups(2).Index + m.Groups(2).Length
            Dim iPoints As Integer() = {iPos1, iPos2}
            oList.Add(iPoints)
        End If
    Next

    Dim sRet As String = ""

    If oList.Count = 1 Then 'One img
        Dim iPoints As Integer() = oList(0)
        Dim sStr1 As String = sHtml.Substring(0, iPoints(0))
        Dim sStr2 As String = sHtml.Substring(iPoints(1))
        sRet = sStr1 & "cid:MyImg0" & sStr2

    ElseIf oList.Count > 1 Then

        For i As Integer = 0 To oList.Count - 1
            Dim iPoints As Integer() = oList(i)
            Dim iPos1 As Integer = iPoints(0)

            If i = 0 Then
                'First img
                Dim sStr1 As String = sHtml.Substring(0, iPos1)
                sRet += sStr1 & "cid:MyImg" & i

            Else 'Rest imgs
                Dim iPrevPos2 As Integer = oList(i - 1)(1)
                Dim sStr1 As String = sHtml.Substring(iPrevPos2, iPos1 - iPrevPos2)
                sRet += sStr1 & "cid:MyImg" & i

                If i = oList.Count - 1 Then    'Last
                    sRet += sHtml.Substring(iPoints(1))
                End If
            End If
        Next
    End If

    If sRet <> "" Then
        Return sRet
    Else
        Return sHtml
    End If
End Function

【讨论】：

它读取 data:image 数据并将这些图像添加为链接资源。