Saat mengirim email pemasaran, akun saya diblokir

Saat ini saya sedang membuat email pemasaran, bermaksud mengirim email massal yang dipersonalisasi ke pelanggan perorangan. Namun, jika beberapa alamat email tidak ada, ada risiko akun MS Office 365 saya diblokir ketika email ini dikembalikan.

Bagaimana menghindari masalah ini, aplikasi ini digunakan untuk pengambilan email massal.

Kesalahan setelah Pentalan:
someemail@abc.com tidak ditemukan di abc.com

Apa yang saya coba:

MailMessage msg = new MailMessage();
            msg.To.Add(new MailAddress(toEmail, recipientName));
            msg.From = new MailAddress(fromEmail, emailConfig.DisplayName);
            msg.Subject = emailSub;
            emailBody = emailBody.Replace("[Name]", recipientName);
            msg.Body = emailBody;
            //attachments//
            var lst = getTemplateAttachments(templateId);
            foreach (var item in lst)
            {
                byte[] bytes = File.ReadAllBytes(item.FilePath);
                MemoryStream ms = new MemoryStream(bytes);
                Attachment data = new Attachment(ms, item.FileName);
                msg.Attachments.Add(data);

            }

            //attachments//
            msg.IsBodyHtml = true;
            msg.BodyEncoding = System.Text.Encoding.UTF8;
            SmtpClient smtpclient = new SmtpClient();
            smtpclient.UseDefaultCredentials = true;
            smtpclient.Credentials = new System.Net.NetworkCredential(emailConfig.FromEmail, emailConfig.Password);
           
            smtpclient.Port = 587; 
            smtpclient.Host = "smtp.office365.com";
           
            smtpclient.DeliveryMethod = SmtpDeliveryMethod.Network;
            smtpclient.EnableSsl = true;
            
            try
            {
                
                smtpclient.Send(msg);
               
                resp.IsSent = true;
                resp.RespMsg = "success";
                return resp;


            }
            catch (Exception ex)
            {}