For a modern IMAP library, check out MailKit

Jun 17, 2015 at 6:35 PM
You can find MailKit at

It is completely free for commercial use and is fully open source as well.

It implements all of the common IMAP extensions (ACL, QUOTA, LITERAL+, IDLE, NAMESPACE, ID, CHILDREN, LOGINDISABLED, STARTTLS, MULTIAPPEND, UNSELECT, UIDPLUS, CONDSTORE, ESEARCH, SASL-IR, COMPRESS, WITHIN, ENABLE, QRESYNC, SORT, THREAD, ESORT, SPECIAL-USE, MOVE, SORT=DISPLAY, SEARCH=FUZZY, UTF8=ACCEPT, UTF8=ONLY, XLIST, and X-GM-EXT1). It has async versions of all blocking API's and each of them supports cancellation via System.Threading.CancellationToken.

It is the best IMAP client library available for .NET. Period.

Supports .NET 4.0 and .NET 4.5.