发送带有c#附件的电子邮件，附件作为第1.2部分的雷鸟

I have a C# application which emails out Excel spreadsheet reports via an Exchange 2007 server using SMTP. These arrive fine for Outlook users, but for Thunderbird and Blackberry users the attachments have been renamed as "Part 1.2".I have a C# application which emails out Excel