SMTP client with MIME attachment

public static string SendMessageWithAttachment(string sendTo, string sendFrom, string sendSubject, string sendMessage, ArrayList attachments,string Username,string Password)
        {
            try 
            {
                bool bTest = ValidateEmailAddress(sendTo);
                if (bTest == false)
                {
                    return "Invalid recipient email address: " + sendTo;
                }
                MailMessage message = new MailMessage(sendFrom, sendTo, sendSubject, sendMessage);
                message.From = new MailAddress(sendFrom);
                foreach (string attach in attachments)
                {
                Attachment attached=new Attachment(attach,MediaTypeNames.Application.Octet);
                    message.Attachments.Add(attached);
                }
                SmtpClient client=new SmtpClient();
                if (bTest == true)
                {
                    message.To.Add(new MailAddress(sendTo));
                    message.Subject = sendSubject;
                    message.BodyEncoding = System.Text.Encoding.UTF8;
                    client.UseDefaultCredentials = false;
                    System.Net.NetworkCredential NetworkCred = new System.Net.NetworkCredential("", "");
                    NetworkCred.UserName = Username;
                    NetworkCred.Password = Password;
                    client.Host = "smtp.gmail.com";
                    client.Port = 587;
                    client.EnableSsl = true;
                    client.Send(message);
                    return "Message sent to " + sendTo + " at " + DateTime.Now.ToString() + ",";
                }
            }
            catch(Exception ex)
            {
                System.Diagnostics.Debug.WriteLine(ex.ToString());
                
            }
        }
        public static bool ValidateEmailAddress(string emailAddress)
        {
            try
            {
                string TextToValidate = emailAddress;
                Regex expression = new Regex("(?<user>[^@]+)@(?<host>.+)");
                if (expression.IsMatch(TextToValidate))
                {
                    return true;
                }
                else
                {
                    return false;
                }
             }
             catch(Exception)
                {
                    throw;
                }
            
        } 


private void btnSend_Click(object sender, EventArgs e)
       {
           this.Cursor = Cursors.WaitCursor;
Regex emailregex = new Regex("("?<user>[^@]+)@(?<host>.+)");
           Match m = emailregex.Match(tbTo.Text);
           string User = m.Groups["user"].Value;
           string[] arr = txtAttachment.Text.Split(";");
           alAttachments = new ArrayList();
           for(int i=0;i<arr.Length;i++)
           {
               if((String.IsNullOrEmpty(arr[i].ToString().Trim())!=null)||(String.IsNullOrEmpty(arr[i].ToString().Trim())!=String.Empty))
               {
                   alAttachments.Add(arr[i].ToString().Trim());
               }
           }
string result=EmailHandler.Emailer.SendMessage(tbTo.Text,tbxFrom.Text,tbSubject.Text,MessageBody.Text,User,);
                MessageBox.Show(result,"Email Transmittal";);
                this.Cursor = Cursors.Default;
        }
</host></user>