从Windows SMTP服务读取EML文件。有什么理由不使用StreamReader？

I'm going to be reading and parsing the EML files dropped by the Microsoft SMTP service. I am a newbie to using the various stream classes. The implementation I have seen that parses these files uses a variation on System.IO.Stream to read byte by byte. However, it seems like these files should never be anything but text. Wouldn't it be better to use a StreamReader? And if so, is there any reason to use something other than the default (UTF-8) encoding?I'm going to be reading and parsing the EML fil