Send an e-mail from .NET Core 2.1+

SendMail.cs

using System.Net;
using System.Net.Mail;

namespace testemail
{
    public static class SendMailer  
    {
        public static void SendMail(EmailDTO dto)
        {
            SmtpClient client = new SmtpClient(dto.address);

            if (!string.IsNullOrEmpty(dto.username))
            {
                client.UseDefaultCredentials = false;
                client.Credentials = new NetworkCredential(dto.username, dto.password);
            }
            client.DeliveryFormat = SmtpDeliveryFormat.International;
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            client.Host = dto.address;
            client.Port = dto.portNumber;

            MailMessage mailMessage = new MailMessage();
            mailMessage.From = new MailAddress(dto.from);
            mailMessage.Body = dto.body;
            mailMessage.Subject = dto.subject;

            foreach (var e in dto.replytolist) if (!string.IsNullOrWhiteSpace(e)) mailMessage.ReplyToList.Add(new MailAddress(e));
            foreach (var e in dto.tolist) if (!string.IsNullOrWhiteSpace(e)) mailMessage.To.Add(new MailAddress(e));
            foreach (var e in dto.cclist) if (!string.IsNullOrWhiteSpace(e)) mailMessage.CC.Add(new MailAddress(e));

            client.Send(mailMessage);
        }

    }
}