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 web界面中的内嵌图像:

工作电子邮件的相关原始邮件标题和原始正文部分:

--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:工作原始电子邮件.

但是,当我通过它发送这样的电子邮件时System.Net.Mail,.NET它不能在gmail web界面中工作,而是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:非工作原始电子邮件.

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:我怎么办错误,GMail不显示我的内嵌图像？我如何更改代码？也许我想要的东西无法实现System.Net.Mail？

Answer 1

当作为附件添加时，内嵌图像在 GMail 网络界面中被忽略。将图像添加为备用视图时，它会被 Outlook 忽略。

要添加与 GMail 网络界面和 Outlook（和 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

我对 Pyhon (Django) 也有同样的问题。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 3

我遇到了同样的问题（在 Java 中，对于 C# 来说也是如此）。\n通过在 \xe2\x80\x9c<\xe2\x80\x9d 和 \xe2\x80\x9c>\xe2\x80\x9d 之间添加 contentId 来解决

\n\n

\n\n

该软件适用于 Gmail、yahoo 和 Outlook。

\n