GemBox.Email
.NET Email Library

static void Main()
{
    // If using the Professional version, put your serial key below.
    ComponentInfo.SetLicense("FREE-LIMITED-KEY");

    // Create new IMAP client.
    using var imap = new ImapClient("<ADDRESS> (e.g. imap.gmail.com)");
    
    // Connect to IMAP server.
    imap.Connect();

    // Authenticate using the credentials; username and password.
    imap.Authenticate("<USERNAME>", "<PASSWORD>");
}