添加为 smtp 的 MailAttachment 后无法正确呈现 Exchange 电子邮件附件

Question

我需要将 EmailMessage 转换为 MailMessage 以用于 smtp 邮件发送。但如果附件是 .docx、.txt、.jpg 等文件，它会正确显示。我面临的问题是，每当 EmailMessage 包含电子邮件附件 (.msg) 时，附件就会变成字符串 /stream(Image2)。我添加了附件对象属性的屏幕截图（Image3）。

问题： 我需要在代码中添加什么来确保附件与来自 Microsoft Exchange 电子邮件的原始附件完全相同，例如预期结果 Image1？

Image1：smtp 发送后附件的样子。

图2：smtp邮件发送后附件结果。

Image3：附件属性截图

我的代码如下：

MailMessage message = new MailMessage();
EmailMessage msg = new EmailMessage(service); //service is Microsoft.Exchange.WebServices.Data
MemoryStream ms = new MemoryStream();
            
PropertySet propSet = new PropertySet(BasePropertySet.FirstClassProperties,ItemSchema.Attachments, EmailMessageSchema.NormalizedBody, EmailMessageSchema.TextBody);
propSet.RequestedBodyType = BodyType.HTML;
propSet.BlockExternalImages = false;
msg = EmailMessage.Bind(service, emailId, propSet);

foreach (Microsoft.Exchange.WebServices.Data.Attachment attachment in msg.Attachments){  
    if (attachment is FileAttachment)
    {
        // Attachments such as .txt, .docx, .xlsx
        // This code block for FileAttachment is totally working fine.
        FileAttachment fileAttachment = attachment as FileAttachment;
        if (fileAttachment != null)
        {
            fileAttachment.Load();
            ms = new MemoryStream(fileAttachment.Content);
            attachmentName = fileAttachment.Name;
            System.Net.Mail.Attachment att = new System.Net.Mail.Attachment(ms, attachmentName);
            message.Attachments.Add(att);
        }
    }
    else if (attachment is ItemAttachment)
    {
        //This is where the EmailMessage attachment gets converted to MailMessage attachment
        //Attachment is .msg
        //The result here becomes random strings
        ItemAttachment itemAttachment = attachment as ItemAttachment;
        if (itemAttachment != null)
        {
             itemAttachment.Load(new PropertySet(ItemSchema.MimeContent));
             byte[] itemContent = itemAttachment.Item.MimeContent.Content.ToArray();
             ms = new MemoryStream(itemContent);
             attachmentName = itemAttachment.Name;
             System.Net.Mail.Attachment att = new System.Net.Mail.Attachment(ms, attachmentName, attachment.ContentType);
             message.Attachments.Add(att);
        }
    }
}

//Send the MailMessage using SMTP
using (SmtpClient client = new SmtpClient())
{
    client.Host = config.smtp_AmazonAWSHost;
    client.Port = config.portSMTP;
    client.UseDefaultCredentials = false;
    client.Credentials = new NetworkCredential(config.smtp_Username, config.smtp_Password);
    client.EnableSsl = true;
    client.Send(message);
}

Answer 1

看来附加信息

ContentDisposition

是

Inline

而不是

Attachment

。

尝试

System.Net.Mail.Attachment att = new System.Net.Mail.Attachment(ms, attachmentName, attachment.ContentType);

ContentDisposition disposition = att.ContentDisposition;
disposition.Inline = false;

message.Attachments.Add(att);