/// <summary>
        /// Marks message as deleted.
        /// </summary>
        /// <exception cref="ObjectDisposedException">Is raised when this object is disposed and this method is accessed.</exception>
        /// <exception cref="POP3_ClientException">Is raised when POP3 serveer returns error.</exception>
        public void MarkForDeletion()
        {
            if (this.IsDisposed)
            {
                throw new ObjectDisposedException(this.GetType().Name);
            }
            if (this.IsMarkedForDeletion)
            {
                return;
            }
            m_IsMarkedForDeletion = true;

            m_Pop3Client.MarkMessageForDeletion(this.SequenceNumber);
        }