I just found a great little open source project called cpSphere - Email Components. It's available on GotDotNet Workspaces. This little nugget contains classes for POP3 and SMTP.
Over the years I’ve used quite a few commercial components for handling email. My favorite controls are the ones offered by QuikSoft. I’ve used their COM and .NET versions with great success. Arguably, in second place, are the controls from Advanced Intellect. They have a few other products that compliment each other. I've even used the mail control from .NetToolWorks.
I’ve run into parsing problems with each one of these controls. All of these vendors are fairly quick to respond with updates… or excuses. What draws me to the open source project is the ability to jump into the code when there is a parsing problem. The commercial vendors will always have more features to their products but in some cases I don’t need them.
Oh…If you visit the .NetToolWorks site be sure to turn down the sound on your computer. They have a Flash animation that will make you jump out of your boots. Also, the clicking sound on every navigation item will drive you nuts.