I previous wrote an application that required extracting email from GMail via POP3 using C#. Now that same application has gotten a bit more complicated. I need to extract file attachments from the email. I've done Base64 MIME Encoding/Decoding a long time ago. I did not have the inclination to re-do it in C# so I went searching through the 'Net for ready-made code.
There were several open source examples, but the one that suited me best was this one from CodeProject:
For now, I'm just using the decoding part. But I foresee a need to do encoding pretty soon.