GMail没有显示我使用System.Net.Mail发送的内嵌图像（cid）

Question

当我通过outlook或gmail向gmail电子邮件地址发送电子邮件时，我可以添加直接显示在gmail网络界面中的内联图片：

工作电子邮件的相关原始邮件标头和原始部分：

--089e0158b6909948880520cef593
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr">Image there?<div><img src=3D"cid:ii_if3zqhar0_15014363be0a=
41b2" width=3D"10" height=3D"3"><br>=E2=80=8BHope so!<br></div></div>

--089e0158b6909948880520cef593--
--089e0158b69099488c0520cef594
Content-Type: image/png; name="test.png"
Content-Disposition: inline; filename="test.png"
Content-Transfer-Encoding: base64
Content-ID: <ii_if3zqhar0_15014363be0a41b2>
X-Attachment-Id: ii_if3zqhar0_15014363be0a41b2

iVBORw0KGgoAAAANSUhEUgAAAAoAAAADCAIAAAAlXwkiAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJ
bWFnZVJlYWR5ccllPAAAADFJREFUeNpi+A8BDCf/wwDD/1VIbBABIudDmAchokwgag9QAiwHVcsM
Z/5fCdYJEGAAuthJ+AVi5KgAAAAASUVORK5CYII=
--089e0158b69099488c0520cef594--

完整的原始电子邮件：Working raw-email。

但是，当我通过System.Net.Mail从.NET发送此类电子邮件时，它无法在gmail网络界面中运行，而是使用任何其他电子邮件客户端（Outlook，iphone等）：

非工作电子邮件的相关原始邮件标头和原始部分：

----boundary_3_6a0761ee-57e2-4bdd-b1f1-7302b3c8a7a1
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: quoted-printable

Image there?<br /><img src=3D"cid:test.png@71236720.91827344" /><=
br />Hope so!
----boundary_3_6a0761ee-57e2-4bdd-b1f1-7302b3c8a7a1--

----boundary_5_979e00c0-3fb9-46a0-b25c-1cee82cc15eb
Content-Type: image/png; name=test.png
Content-Transfer-Encoding: base64
Content-Disposition: inline; filename=test.png
Content-ID: <test.png@71236720.91827344>

iVBORw0KGgoAAAANSUhEUgAAAAoAAAADCAIAAAAlXwkiAAAAGXRFWHRTb2Z0d2FyZQBB
ZG9iZSBJbWFnZVJlYWR5ccllPAAAADFJREFUeNpi+A8BDCf/wwDD/1VIbBABIudDmAch
okwgag9QAiwHVcsMZ/5fCdYJEGAAuthJ+AVi5KgAAAAASUVORK5CYII=
----boundary_5_979e00c0-3fb9-46a0-b25c-1cee82cc15eb--

完整的非工作原始电子邮件：Nonworking raw-email。

这是我发送内联图片的代码：

SmtpClient client = new SmtpClient("real.server.on.the.internet");
MailMessage mail = new MailMessage("Flattiverse <xxx@flattiverse.com>", "Ghostie <xxx@gmail.com>");
mail.BodyEncoding = System.Text.Encoding.UTF8;
mail.SubjectEncoding = System.Text.Encoding.UTF8;

AlternateView plainView = AlternateView.CreateAlternateViewFromString("Please view as HTML-Mail.", System.Text.Encoding.UTF8, "text/plain");
plainView.TransferEncoding = System.Net.Mime.TransferEncoding.QuotedPrintable;

AlternateView htmlView = AlternateView.CreateAlternateViewFromString("Image there?<br /><img src=\"cid:test.png@71236720.91827344\" /><br />Hope so!", System.Text.Encoding.UTF8, "text/html");
htmlView.TransferEncoding = System.Net.Mime.TransferEncoding.QuotedPrintable;
mail.AlternateViews.Add(plainView);
mail.AlternateViews.Add(htmlView);

mail.Subject = "7";

Attachment attachment = new Attachment("test.png", "image/png");
attachment.ContentId = "test.png@71236720.91827344";
attachment.ContentDisposition.Inline = true;
attachment.ContentDisposition.DispositionType = "inline; filename=test.png";
mail.Attachments.Add(attachment);

client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("working_username", "working_password");
client.Send(mail);

我还尝试了GMail格式的cid（例如ii_012345678_9abcdef0123456789）以及其他相关问题中陈述的许多其他内容。 （在邮件正文中使用'代替'等）

问题：GMail没有显示我的内联图片，我做错了什么？我如何更改代码？也许用System.Net.Mail无法实现我想要的东西？

Answer 1

作为附件添加时，GMail Web界面中会忽略内联图像。将图像添加为备用视图时，Outlook会忽略它。

要添加与GMail webinterface和Outlook（以及iPhone邮件客户端）兼容的内嵌图像，您必须将其添加为LinkedResource。

问题中的示例代码必须像这样修复：

SmtpClient client = new SmtpClient("real.server.on.the.internet");
MailMessage mail = new MailMessage("Flattiverse <info@flattiverse.com>", "Ghostie <matthias.lukaseder.test@gmail.com>");
mail.BodyEncoding = System.Text.Encoding.UTF8;
mail.SubjectEncoding = System.Text.Encoding.UTF8;

LinkedResource image = new LinkedResource("test.png", "image/png");
image.ContentId = "test.png@71236720.91827344";
image.TransferEncoding = System.Net.Mime.TransferEncoding.Base64;
image.ContentType.Name = "test.png@71236720.91827344";
image.ContentLink = new Uri("cid:test.png@71236720.91827344");

AlternateView plainView = AlternateView.CreateAlternateViewFromString("Please view as HTML-Mail.", System.Text.Encoding.UTF8, "text/plain");
plainView.TransferEncoding = System.Net.Mime.TransferEncoding.QuotedPrintable;

AlternateView htmlView = AlternateView.CreateAlternateViewFromString("Image there?<br /><img src=\"cid:test.png@71236720.91827344\" /><br />Hope so!", System.Text.Encoding.UTF8, "text/html");
htmlView.LinkedResources.Add(image);
htmlView.TransferEncoding = System.Net.Mime.TransferEncoding.QuotedPrintable;
mail.AlternateViews.Add(plainView);
mail.AlternateViews.Add(htmlView);

mail.Subject = "15";

client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("working_username", "working_password");
client.Send(mail);

Answer 2

我遇到了同样的问题（在Java中，对于c＃将是相同的）。 通过在“ <”和“>”

之间添加contentId来解决

此人正在使用Gmail，雅虎和Outlook。

Answer 3

我与Pyhon（Django）遇到相同的问题。只需添加X-Attachment-Id标头即可解决此问题：

img.add_header('Content-ID', '<filename.png>')
img.add_header('X-Attachment-Id', 'filename.png')
img.add_header('Content-Disposition', 'inline', filename='filename.png')
message.attach(img)

希望这对某人有帮助：-）

Answer 4

将其添加为 LinkedResource 。

我有一个名为 Confirm_Account_RegistrationInd.html

的模板

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>Bienvenido Email de  {6}</title>
</head>

<body>
    <table width="100%" border="0" cellspacing="0" cellpadding="0">
        <tr>
            <td align="center" valign="top" bgcolor="#fff" style="background-color:lightgray;">
                <br>
                <br>
                <table width="600" border="0" cellspacing="0" cellpadding="0" >
                    <tr>
                        <td height="70" align="left" valign="middle"></td>
                    </tr>
                    <tr>
                        <td align="left" valign="top" bgcolor="#564319" style="background-color:#007ebd; font-family:Arial, Helvetica, sans-serif; padding:10px;">
                            <table>
                                <tr>
                                    <td>
                                        "<img id="logo" src="miimg_id" alt="logo" style="height: 60px; border: 3px solid #007ebd; border-radius: 43px;" />";
                                    </td>
                                    <td>
                                        <div style="font-size:36px; color:#ffffff;">
                                            <b>{0}</b>
                                        </div>
                                        <div style="font-size:13px; color:lightcyan;">
                                            <b>{1} : {6}</b>
                                        </div>
                                    </td>
                                    
                                </tr>
                        </table>
                        </td>
                    </tr>
                    <tr>
                        <td align="left" valign="top" bgcolor="#ffffff" style="background-color:#ffffff;">
                            <table width="100%" border="0" cellspacing="0" cellpadding="0">
                                <tr>
                                    <td align="center" valign="middle" style="padding:10px; color:#564319; font-size:28px; font-family:Georgia, 'Times New Roman', Times, serif;">
                                        ¡Felicitaciones! <small>Estás Registrado.</small>
                                    </td>
                                </tr>
                            </table>
                            <table width="95%" border="0" align="center" cellpadding="0" cellspacing="0">
                                
                                <tr>
                                    <td width="100%" style="color:darkslategrey; font-family:Arial, Helvetica, sans-serif; padding:10px;">
                                        <div style="font-size:16px;">
                                            Apreciad@ {2},
                                        </div>
                                        <div style="font-size:12px;text-align: justify;">
                                            Ha sido creada una cuenta en el sitio.
                                            Todo lo que necesitas es hacer clic en el botón en la parte de abajo (Te tomará solamente un momento)
                                            Este correo es para la verificación de la propiedad del correo elctrónico.
                                            <hr>
                                            <center>

                                                <button type="button" title="Confirmar cuenta" style="background: darkgoldenrod">
                                                    <a href="{5}" style="font-size:22px;  padding: 10px; color: #ffffff">
                                                        Confirmar correo ahora
                                                    </a>
                                                </button>

                                            </center>
                                            <hr>
                                        </div>
                                    </td>
                                </tr>
                            </table>
                            
                            <table width="100%" border="0" align="center" cellpadding="0" cellspacing="0" style="margin-bottom:15px;">
                                <tr>
                                    <td align="left" valign="middle" style="padding:15px; font-family:Arial, Helvetica, sans-serif;">
                                        <div style="font-size:20px; color:#564319;">
                                            <b>Por favor manten tus credenciales seguras, para usarlas en el futuro. </b>
                                        </div>
                                        <div style="font-size:16px; color:#525252;">
                                            <b>Correo         :</b> {3}
                                            <br />
                                            <b>Nombre de usuario :</b> {3}
                                            <br />
                                            {7}
                                            <br />
                                        </div>
                                    </td>
                                </tr>
                            </table>
                            <table width="100%" border="0" cellspacing="0" cellpadding="0">
                                <tr>
                                    <td align="center" valign="middle" style="padding:15px; background-color:#007ebd; font-family:Arial, Helvetica, sans-serif;">

                                        <div style="font-size:20px; color:#fff;">
                                            <b>¡Actualiza tus contraseñas continuamente!</b>
                                        </div>
                                        <br>
                                        <div style="font-size:13px; color:aliceblue;">

                                            <br>


                                        </div>
                                    </td>
                                </tr>
                            </table>
                           
                        </td>
                    </tr>
                    
                </table>
                <br>
                <br>
            </td>
        </tr>
    </table>
</body>
</html>

我要显示的图像：

"<img id="logo" src="miimg_id" alt="logo" style="height: 60px; border: 3px solid #007ebd; border-radius: 43px;" />";

您可以看到src属性的值为 miimg_id

在视图中，我具有可以填充 {}

的值

我有方法，在获取数据以填充值之后，我将以字符串形式读取视图，称为 ReSendEmailAsync

[HttpPost]
        public async Task<IActionResult> ReSendEmailAsync([FromBody] string id)
        {
            string returnUrl = null;
            returnUrl = returnUrl ?? Url.Content("~/");

            string empleadoNombre = "";
            string attach = "";
            string logoName = "logo_dif.png";


            var user = await _unitOfWork.ApplicationUser.GetFirstOrDefaultAsync(u => u.Id == int.Parse(id), includeProperties: "Empleado");

            if (user == null)
            {
                return Json(new { success = false, message = "Usuario Email" });
            }
            if (user.EmailConfirmed)
            {
                return Json(new { success = true, message = "Cuenta ya fue confirmada" });
            }

            try
            {
                empleadoNombre = user.Empleado.Nombre;
            }
            catch (Exception e)
            {

            }

            var code = await _userManager.GenerateEmailConfirmationTokenAsync(user).ConfigureAwait(true);
            code = WebEncoders.Base64UrlEncode(Encoding.UTF8.GetBytes(code));
            var callbackUrl = Url.Page(
                "/Account/ConfirmEmail",
                pageHandler: null,
                values: new { area = "Identity", userId = user.Id, code = code, returnUrl = returnUrl },
                protocol: Request.Scheme);

            //Customizde email
            var PathToFile = _webHostEnvironment.WebRootPath + Path.DirectorySeparatorChar.ToString()
                + "Templates" + Path.DirectorySeparatorChar.ToString()
                + "EmailTemplates" + Path.DirectorySeparatorChar.ToString()
                + "Confirm_Account_RegistrationInd.html";

            var subject = "Confirmar Registro de cuenta";
            string HtmlBody = "";

            using (StreamReader streamReader = System.IO.File.OpenText(PathToFile))
            {
                HtmlBody = streamReader.ReadToEnd();
            }

        //{0} Subject
        //{1} DateTime
        //{2} Name
        //{3} Email
        //{4} Messaje
        //{5} CallBack
        //{6} AppName
        //{7} Pass

                // logo as attach
                var PathToImage = _webHostEnvironment.WebRootPath + Path.DirectorySeparatorChar.ToString()
                + "Templates" + Path.DirectorySeparatorChar.ToString()
                + "EmailTemplates" + Path.DirectorySeparatorChar.ToString()
                + logoName;

                attach = PathToImage;


            string message = $"Por favor confirme su cuenta <a href='{HtmlEncoder.Default.Encode(callbackUrl)}'>Clic Aquí</a>.";
            string messageBody = string.Format(HtmlBody,
                subject,
                String.Format("{0:dddd, d MMMM yyyy}", DateTime.Now),
                empleadoNombre,
                user.Email,
                message,
                callbackUrl,
                "Indicadores",
                ""
             );

            try
            {
                MailRequest mailRequest = new MailRequest();

                mailRequest.Body = messageBody;
                mailRequest.ToEmail = user.Email;
                mailRequest.Subject = "Confirmar su correo";
                mailRequest.Attachments = new List<MailAttachment> 
                { new MailAttachment{
                    Name = logoName,
                    Path = attach
                } };

                await _mailService.SendEmailAsync(mailRequest);
            }
            catch(Exception e)
            {
                return Json(new { success = false, message = "Al enviar email" });
            }

            return Json(new { success = true, message = "Operación exitosa" });
        }

在我的班级 MailService

主要方法是 SendEmailAsync ，我将值传递给 MailMessage对象

但是我有另一个名为 Mail_Body 的方法，该方法返回 AlternateView 对象

public class MailService : IMailService
    {
        private readonly MailSettings _mailSettings;
        public MailService(IOptions<MailSettings> mailSettings)
        {
            _mailSettings = mailSettings.Value;
        }

        public async Task SendEmailAsync(MailRequest mailRequest)
        {
            MailMessage message = new MailMessage();
            SmtpClient smtp = new SmtpClient();
            message.From = new MailAddress(_mailSettings.UserName);
            message.To.Add(new MailAddress(mailRequest.ToEmail));
            message.Subject = mailRequest.Subject;
            message.BodyEncoding = System.Text.Encoding.UTF8;
            message.SubjectEncoding = System.Text.Encoding.UTF8;
            if (mailRequest.Attachments != null)
            {
                //int i = 0;
                foreach (var attachmentStr in mailRequest.Attachments)
                {
                    message.AlternateViews.Add(Mail_Body(mailRequest.Body, attachmentStr.Path, attachmentStr.Name));

                }
            }
            message.IsBodyHtml = true;
            smtp.Port = _mailSettings.Port;
            smtp.Host = _mailSettings.Host;
            smtp.EnableSsl = _mailSettings.EnableSSL;
            smtp.UseDefaultCredentials = false;
            smtp.Credentials = new NetworkCredential(_mailSettings.UserName, _mailSettings.Password);
            smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
            await smtp.SendMailAsync(message);
        }

        private AlternateView Mail_Body(string strr, string path, string contentId)
        {

            LinkedResource Img = new LinkedResource(path, "image/png");
            Img.ContentId = "logo_img";

            strr = strr.Replace("\"miimg_id\"", "cid:logo_img");

            AlternateView AV =
            AlternateView.CreateAlternateViewFromString(strr, null, MediaTypeNames.Text.Html);
            AV.LinkedResources.Add(Img);
            return AV;
        }
    }

徽标图像称为logo_dif.png，位于

最终结果为gmail：