使用.NET C#我想从 *.msg文件加载Outlook HTML消息，添加收件人并将其保存到标准草稿文件夹。
我无法正确地使用Outlook 2019（不是2016年或2013年），因为保存后，它将消息正文格式转换为纯文本。这仅适用于2019版本。在代码示例中，我首先创建电子邮件并将其保存为草稿。直到COM应用程序对象示例化，格式仍为html。就在我手动打开Outlook之后。exe的消息已转为纯文本。我检查这与函数PrintBodyFormat。请注意，这种情况只发生在Office 2019。

using Debug = System.Diagnostics.Debug;
using Outlook = Microsoft.Office.Interop.Outlook;

static void CreateMail()
{
    Outlook.Application app = new Outlook.Application();
    Outlook.MailItem mail = app.CreateItemFromTemplate(@"C:\html_message.msg");
    mail.Recipients.Add("johndoe@foobar.com");

    Debug.WriteLine(mail.BodyFormat.ToString());
    //OUTPUT WITH ALL OUTLOOK VERSION: "olFormatHTML"

    mail.Save();
    mail.Close(Outlook.OlInspectorClose.olDiscard);
    System.Runtime.InteropServices.Marshal.ReleaseComObject(mail);
    mail = null;

    Outlook.NameSpace nms = app.GetNamespace("MAPI");
    Outlook.MAPIFolder DraftFolder = nms.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderDrafts);
    mail = DraftFolder.Items[1];

    Debug.WriteLine(mail.BodyFormat.ToString());
    //OUTPUT WITH ALL OUTLOOK VERSION: "olFormatHTML"

    mail.Close(Outlook.OlInspectorClose.olDiscard);
    System.Runtime.InteropServices.Marshal.ReleaseComObject(mail);
    mail = null;
    app.Quit();
    System.Runtime.InteropServices.Marshal.ReleaseComObject(DraftFolder);
    System.Runtime.InteropServices.Marshal.ReleaseComObject(nms);
    System.Runtime.InteropServices.Marshal.ReleaseComObject(app);
}

//Run this after manually opened Outlook.exe 
static void PrintBodyFormat()
{
    Outlook.Application app = new Outlook.Application();
    Outlook.NameSpace nms = app.GetNamespace("MAPI");
    Outlook.MAPIFolder DraftFolder = nms.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderDrafts);
    Outlook.MailItem mail = DraftFolder.Items[1];

    Debug.WriteLine(mail.BodyFormat.ToString());
    //OUTPUT WITH OUTLOOK 2016 OR EARLIER: "olFormatHTML"
    //OUTPUT WITH OUTLOOK 2019: "olFormatPlain"

    app.Quit();
    System.Runtime.InteropServices.Marshal.ReleaseComObject(mail);
    System.Runtime.InteropServices.Marshal.ReleaseComObject(DraftFolder);
    System.Runtime.InteropServices.Marshal.ReleaseComObject(nms);
    System.Runtime.InteropServices.Marshal.ReleaseComObject(app);
}