Sending emails with .Net Core using MailKit with DKIM signature

EMailerService.cs

using System;
using MailKit.Net.Smtp;
using MailKit.Security;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Logging;
using MimeKit;
using MimeKit.Cryptography;

namespace MailerApi.Services
{
    public class EmailerService
    {
        private readonly ILogger<EmailerService> Logger;
        IConfigurationSection SMTP { get; }
        DkimSigner Signer { get; set; }

        public EmailerService(
            IConfiguration config,
            ILogger<EmailerService> logger
        )
        {
            Logger = logger;

            try
            {
                // Used to access appsettings.json
                SMTP = config.GetSection("smtp");
            }
            catch (System.Exception ex)
            {
                Logger.LogError(ex, ex.Message);
            }
        }

        public void Send(string toName, string toMail, string subject, string body, string bodyHtml)
        {
            try
            {
                Signer = new DkimSigner(
                    "data/dkimkey.txt", // path to your privatekey
                    "mydomain.org", // your domain name
                    "654321.mydomain") // The selector given on https://dkimcore.org/
                {
                    HeaderCanonicalizationAlgorithm = DkimCanonicalizationAlgorithm.Simple,
                    BodyCanonicalizationAlgorithm = DkimCanonicalizationAlgorithm.Simple,
                    AgentOrUserIdentifier = "@mydomain.org", // your domain name
                    QueryMethod = "dns/txt",
                };

                // Composing the whole email
                var message = new MimeMessage();
                message.From.Add(new MailboxAddress(SMTP["FromName"], SMTP["From"]));
                message.To.Add(new MailboxAddress(toName, toMail));
                message.Subject = subject;

                var headers = new HeaderId[] { HeaderId.From, HeaderId.Subject, HeaderId.To };

                var builder = new BodyBuilder();
                builder.TextBody = body;
                builder.HtmlBody = bodyHtml;

                message.Body = builder.ToMessageBody();
                message.Prepare(EncodingConstraint.SevenBit);

                Signer.Sign(message, headers);

                // Sending the email
                using(var client = new SmtpClient())
                {
                    // For demo-purposes, accept all SSL certificates (in case the server supports STARTTLS)
                    client.ServerCertificateValidationCallback = (s, c, h, e) =>
                    {
                        Console.WriteLine(e);
                        return true;
                    };

                    client.Connect(SMTP["Url"], Convert.ToInt32(SMTP["Port"]), SecureSocketOptions.SslOnConnect);
                    client.Authenticate(SMTP["Login"], SMTP["Password"]);

                    client.Send(message);
                    client.Disconnect(true);
                }
            }
            catch (System.Exception ex)
            {
                Logger.LogError(ex, ex.Message);
            }
        }
    }
}