我试图发送包含使用 SmtpClient 和 MailMessage 类非ASCII字符的电子邮件。

I am trying to send emails that contain non-ASCII characters using the SmtpClient and MailMessage classes.

我使用一个外部邮件服务（ MailChimp ）和我的一些电子邮件已经拒绝了他们的SMTP服务器。我曾接触过他们，这是他们的回答是：

I am using an external mailing service (MailChimp) and some of my emails have been rejected by their SMTP server. I have contacted them and this is what they replied:

它出现在主题行正在Base64的EN codeD，然后引用打印连接codeD，通常要细，但人物之一，被两行打破。所以，当你的主题行的时间长一点，才能被正确处理，它的破两行。当使用UTF-8引用的可打印在一个主题行，字符串不应该字里行间被打破。取而代之的是线应短，这样完整的字符串仍然在一起。在这种情况下，没有发生，使重$ P $字符的字符串psents单个字符被多行打破，因此它不是有效的UTF-8引用可打印连接codeD

It appears the subject line is being Base64 encoded and then Quoted-Printable encoded, which generally should be fine, but one of the characters is being broken across two lines. So when your subject lines are a bit longer, in order to be processed correctly, it's broken on to two lines. When using UTF-8 quoted printable in a subject line, character strings aren't supposed to be broken between lines. Instead a line should be shorted so that the full character string remains together. In this case, that's not happening, so the string of characters that represents a single character is being broken across multiple lines, and therefore isn't validly UTF-8 quoted-printable encoded.

有问题的主题是以下内容：

The problematic subject is the following:

Subject: XXXXXXX - 5 personnes vous ont nommé guide

这是在UTF-8 / Base64的：

Which is, in UTF-8/Base64:

Subject: WFhYWFhYWCAtIDUgcGVyc29ubmVzIHZvdXMgb250IG5vbW3DqSBndWlkZQ==

由于该头将超过特定的最大长度（我不能确定是否是引用打印编码和每行76个字符，或者SMTP头限制它的极限），编码和分割之后，首标将变成：

Because that header would exceed a certain maximum length (I am unsure whether it is the Quoted-Printable encoding and its limit of 76 characters per line, or the SMTP header limit), after encoding and split, the header will become:

Subject: =?utf-8?B?WFhYWFhYWCAtIDUgcGVyc29ubmVzIHZvdXMgb250IG5vbW3D?=
 =?utf-8?B?qSBndWlkZQ==?=

显然，这在解码时（因为第一线不能去coded到一个有效的字符串）会导致一个问题。我不知道我完全理解这个问题，我有以下问题：

Apparently this causes an issue when decoding (because the first line cannot be decoded to a valid string). I am not sure I fully understand the problem, and I have the following questions:

另外请注意，一些其他SMTP服务器会接受此消息，不过，这并不意味着它是有效的。

Also note that some other SMTP servers will accept this message, though that does not mean it is valid.

作为一种解决办法，我已经试过禁用Base64编码，这显然是不必要的，但是MailMessage类有一个BodyTransferEncoding属性控制此编码，但只适用于消息的主体部分。无属性似乎能控制对象的转让的编码。

As a workaround, I have tried disabling the Base64 encoding, which apparently is unnecessary, however the MailMessage class has a BodyTransferEncoding property that controls this encoding, but only for the body part of the message. No property seems to control the "transfer" encoding of the subject.

推荐答案

本被确认为在MSDN论坛中的错误： http://social.msdn.microsoft.com/Forums/vstudio/en-US/4d1c1752-70ba-420a-9510-8fb4aa6da046/subject-encoding-on-smtpclientmailmessage

This was confirmed as a bug in the MSDN forums: http://social.msdn.microsoft.com/Forums/vstudio/en-US/4d1c1752-70ba-420a-9510-8fb4aa6da046/subject-encoding-on-smtpclientmailmessage

和一个错误的提交Microsoft连接： https://connect.microsoft.com/VisualStudio/feedback/details/785710/mailmessage-subject-incorrectly-en$c$cd-in-utf-8-base64

And a bug was filed on Microsoft Connect: https://connect.microsoft.com/VisualStudio/feedback/details/785710/mailmessage-subject-incorrectly-encoded-in-utf-8-base64

一个解决办法是到MailMessage的SubjectEncoding设置为其他编码，如ISO-8859-1。在这种情况下，这个问题将成为连接中引用Printable（不是Base64的）codeD这就避免了这个问题。

One work-around is to set the SubjectEncoding of the MailMessage to an other encoding, such as ISO-8859-1. In this case, the subject will be encoded in Quoted Printable (not Base64) which avoids the problem.