Polling a email using async / await
I would rather do smth. like that (I added CancellationToken in case you would want to be able to cancel email parsing while it's in progress):

private static TimeSpan timeToWait = TimeSpan.FromSeconds(30);

//somewhere in your code:
_cancellationTokenSource = new CancellationTokenSource();

private static void Main(string[] args)
{
    CancellationToken token = _cancellationTokenSource.Token;
    do
    {
        try
        {
            ProcessEmailsAndWaitAsync(token).Wait();
        }
        catch (Exception e)
        {
            Debug.WriteLine("&lt;p&gt;Error in Client&lt;/p&gt; &lt;p&gt;Exception&lt;/p&gt; &lt;p&gt;" + e.Message + "&lt;/p&gt;&lt;p&gt;" + e.StackTrace + "&lt;/p&gt; ");
        }
    } while (!token.IsCancellationRequested);
}

private static async Task ProcessEmailsAndWaitAsync(CancellationToken token)
{
    await ProcessMailMessages(token);
    await Task.Delay(timeToWait, token);
}

private static async Task ProcessMailMessages(CancellationToken token)
{
    //...............................................................................
}