看看这个项目:SourceForge上的http://sourceforge.net/projects/hpop/.
It is a free, open source .NET Class library in C# for communicating with POP3 Servers(retrieve/delete messages and attachments). Supports decoding files in Base64/QP encoding, including attachemnts, MS-TNEF format, and MS mht file. Compiles on Mono, DotGNU and .NET framework