I don't see why would you need any books.
Anyway, I don't know your level and cannot assume any information on your knowledge and level of understanding of things. What if you need to read a book on just .NET and C#? Well, you also need to know threading,
System.IO
, networking and UI pretty well.
So, I would only recommend what to use. Let's assume you want to use some SMPT server and some POP3 server. For using a SMTP server, everything is available in .NET FCL:
http://msdn.microsoft.com/en-us/library/system.net.mail.smtpclient%28v=vs.110%29.aspx[
^],
http://msdn.microsoft.com/en-us/library/system.net.mail.mailmessage%28v=vs.110%29.aspx[
^],
http://msdn.microsoft.com/en-us/library/system.net.mail%28v=vs.110%29.aspx[
^],
http://msdn.microsoft.com/en-us/library/gg145039%28v=vs.110%29.aspx[
^].
To work with POP3 or IMAP, you would need to implement the protocol and, the biggest part of the work, parse the mail package and all its part according to different MIME types. I would recommend open-source
http://sourceforge.net/projects/hpop[
^].
This product is not written very well, but it does meticulously follow this huge set of standards. You can use it even if you are not going to implement a POP3 client specifically. (And the code of such client can be just tiny part of the whole work.)
You can also considering using IMAP or something else. Then perform the Web search and try to find appropriate information and some available open-source components which could help you. At this moment, I don't know a good open-source IMAP component (proprietary ones are readily available, but I never tried any), but you can look for them:
http://bit.ly/UHorn2[
^].
After all, you can simple learn the protocol (it is not too difficult) and implement it by yourself. In all cases, the code from OpenPOP.NET can still be used, just without (or with) POP3 protocol implementation itself.
See also:
http://en.wikipedia.org/wiki/E-mail[
^],
http://en.wikipedia.org/wiki/MIME[
^],
http://en.wikipedia.org/wiki/E-mail_client[
^],
http://en.wikipedia.org/wiki/SMTP[
^],
http://en.wikipedia.org/wiki/POP3[
^],
http://en.wikipedia.org/wiki/IMAP[
^].
If your level is good enough to understand all the documentation referenced above and have enough of programming skills, you can implement your system without reading any books. If not, reading a book "for it" would not help much; instead, you would need to learn programming.
—SA