Mail not delivered with colon

using System.Net.Mail;

public static void Send(NotificationMessage message)
        {
            MailMessage objMessage = new MailMessage()
            {
                From = new MailAddress(ConfigurationManager.AppSettings["Email.Sender"]),
                Subject = message.Subject,
                BodyEncoding = Encoding.UTF8,
                IsBodyHtml = true,
                Body = message.MessageBody,
            };

            foreach (var recipient in message.RecipientName)
                objMessage.To.Add(recipient);

            SmtpClient SmtpMail = new SmtpClient(ConfigurationManager.AppSettings["Email.ServerName"]);
            SmtpMail.Send(objMessage);
        }