我通过System.Net.Mail发送的Gmail不显示内嵌图像(CID) [英] GMail not showing inline-images (cid) i'm sending with System.Net.Mail

问题描述

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网络界面中的内嵌图像:

When I send an email via outlook or gmail to a gmail email address I can add inline-images which are directly shown in the gmail webinterface:

工作电子邮件的相关原始邮件标题和原始正文部分:

Relevant raw mail-header and raw body parts of the working email:

--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--

可以正常工作的原始电子邮件:可以工作的原始电子邮件.

Full working raw email: Working raw-email.

但是，当我从.NET通过System.Net.Mail发送这样的电子邮件时，它无法在gmail网络界面中使用，但无法在其他电子邮件客户端(outlook，iphone等)中使用:

However, when I send such an email via System.Net.Mail from .NET it is not working in the gmail webinterface but any other email client (outlook, iphone, etc.):

无效电子邮件的相关原始邮件标题和原始正文部分:

Relevant raw mail-header and raw-body parts of non-working email:

----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--

全部无效的原始电子邮件:无效的原始电子邮件.

Full non-working raw email: Nonworking raw-email.

这是我发送内嵌图像的代码:

This is my code to send inline-images:

SmtpClient client = new SmtpClient("real.server.on.the.internet");
MailMessage mail = new MailMessage("Flattiverse <[e-mail]>", "Ghostie <[e-mail]>");
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提到的许多其他内容. (在邮件正文中使用代替"，等等.)

I also tried cid in GMail format (eg. ii_012345678_9abcdef0123456789) and many other things stated in other related questions. (Using ' instead of " in mail body, etc.)

问题:GMail不显示我的内嵌图像，这是我做错了什么?我该如何更改我的代码?也许我想要的System.Net.Mail无法实现?

Question: What am I doing wrong that GMail doesn't display my inline-images? How do I need to change my code? Maybe what I want can't be achieved with System.Net.Mail?

推荐答案

当作为附件添加时，GMail Web界面中的内嵌图像将被忽略.将图像添加为备用视图时，Outlook会忽略它.

The inline-image is ignored in GMail webinterface when added as attachment. When adding the image as alternate view it gets ignored by Outlook.

要添加与GMail Web界面和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.

To add an inline-image compatible to GMail webinterface and Outlook (and iPhone mail client) you have to add it as LinkedResource.

问题中的示例代码必须像这样固定:

The example code in the question must be fixed like this:

SmtpClient client = new SmtpClient("real.server.on.the.internet");
MailMessage mail = new MailMessage("Flattiverse <[e-mail]>", "Ghostie <[e-mail]>");
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);

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