Pass more value splited with comma in targetAddress parameter of SendMessage.
Sample code to send mail to multiple persons:
public bool SendEmail()
{
    bool status = false;
        try
        {
            //code to send email
            this._mail = new MailMessage();
            this._mail.From = new MailAddress(this.From, this.DisplayName);
            if (!string.IsNullOrEmpty(this.To))
            {
                var distinctAddress = new List<string>(this.To.Split(',').Distinct());
                this.To = string.Empty;
                foreach (string address in distinctAddress) // Loop through all strings
                {
                    this.To += address + ","; // Append string to StringBuilder
                }
                this.To = this.To.TrimEnd(',');
                this._mail.To.Add(this.To);
            }
            if (!string.IsNullOrEmpty(this.CC))
                this._mail.CC.Add(this.CC);
            if (!string.IsNullOrEmpty(this.BCC))
                this._mail.Bcc.Add(this.BCC);
            this._mail.Subject = this.Subject;
            this._mail.IsBodyHtml = this.IsBodyHtml;
            this._mail.Body = this.Body;
            if (this.Priority == true)
            {
                this._mail.Priority = MailPriority.High;
            }
            this._mail.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
            if (this._attachments != null && this._attachments.Count > 0)
            {
                foreach (string file in this._attachments)
                {
                    Attachment attachment = new Attachment(file);
                    this._mail.Attachments.Add(attachment);
                }
            }
            this._smtpServer = new SmtpClient(this.EmailServer);
            this._smtpServer.EnableSsl = this.EnableSsl;
            this._smtpServer.Port = this.Port;
            this._smtpServer.Credentials = new System.Net.NetworkCredential(this.UserId, this.Password);
            if (String.IsNullOrEmpty(this.To) != true || string.IsNullOrEmpty(this.CC) != true || string.IsNullOrEmpty(this.BCC) != true)
                this._smtpServer.Send(this._mail);
            status = true;
        }
        catch (Exception ex)
        {
        }
    return status;
}
1
solved How to send mail through more person from this code?