How to get only unread Mails from inbox using C#?

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Hi, I need to get unread emails from my inbox - to handle bounce-backs messages.
I don't need to get entire message. What I need is only: Subject and body only from unread e-mails.

I probably have to use IMAP, so could recommend me an "open-source" and good solution? so I can sell this software without any problems?

But, when smtp server don't support IMAP, I have to use POP3? That project will be good for that? Or maybe there is some other, better way ?

Thanks for help,

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UPDATE:
I've got an idea.
I can read how many messages are in inbox. So, I also can get the last one.
I can check if there is a bounce-back message in timer (every 5 minutes for example). I could get messages one by one, and check the date. If the message was sent before 5 min ago, i would break.
In that solution, I will not get all messages from an inbox every time. Is that good solution ?

The pseudo-code of my idea:

TIMER( Tick every 5minutes )
{
    (LOCK)
    loop(on inbox from end to begin)
    {
        // If the message date is older then "5 minutes ago" break
        if (message date < DateTime.Now.AddMinutes(-5);)
        {
            if (the subject is "Undelivered Mail Returned to Sender")
            {
                // Here I will parse message so that I will know the addresse
                // And removie that addresse from my list.
            }
        }
        else
            break;
    }
    (UNLOCK)
}