System.Net.Mail.SmtpClient.SendAsync C# (CSharp) Method

        public void SendAsync(MailMessage message, object userToken)
        {
            if (_disposed)
            {
                throw new ObjectDisposedException(GetType().FullName);
            }

            if (NetEventSource.IsEnabled) NetEventSource.Enter(this, message, userToken, _transport);

            try
            {
                if (InCall)
                {
                    throw new InvalidOperationException(SR.net_inasync);
                }

                if (message == null)
                {
                    throw new ArgumentNullException(nameof(message));
                }

                if (DeliveryMethod == SmtpDeliveryMethod.Network)
                    CheckHostAndPort();

                _recipients = new MailAddressCollection();

                if (message.From == null)
                {
                    throw new InvalidOperationException(SR.SmtpFromRequired);
                }

                if (message.To != null)
                {
                    foreach (MailAddress address in message.To)
                    {
                        _recipients.Add(address);
                    }
                }
                if (message.Bcc != null)
                {
                    foreach (MailAddress address in message.Bcc)
                    {
                        _recipients.Add(address);
                    }
                }
                if (message.CC != null)
                {
                    foreach (MailAddress address in message.CC)
                    {
                        _recipients.Add(address);
                    }
                }

                if (_recipients.Count == 0)
                {
                    throw new InvalidOperationException(SR.SmtpRecipientRequired);
                }

                try
                {
                    InCall = true;
                    _cancelled = false;
                    _message = message;
                    string pickupDirectory = PickupDirectoryLocation;

                    CredentialCache cache;
                    // Skip token capturing if no credentials are used or they don't include a default one.
                    // Also do capture the token if ICredential is not of CredentialCache type so we don't know what the exact credential response will be.
                    _transport.IdentityRequired = Credentials != null && (ReferenceEquals(Credentials, CredentialCache.DefaultNetworkCredentials) || (cache = Credentials as CredentialCache) == null || IsSystemNetworkCredentialInCache(cache));

                    _asyncOp = AsyncOperationManager.CreateOperation(userToken);
                    switch (DeliveryMethod)
                    {
                        case SmtpDeliveryMethod.PickupDirectoryFromIis:
                            throw new NotSupportedException(SR.SmtpGetIisPickupDirectoryNotSupported);

                        case SmtpDeliveryMethod.SpecifiedPickupDirectory:
                            {
                                if (EnableSsl)
                                {
                                    throw new SmtpException(SR.SmtpPickupDirectoryDoesnotSupportSsl);
                                }

                                _writer = GetFileMailWriter(pickupDirectory);
                                bool allowUnicode = IsUnicodeSupported();
                                ValidateUnicodeRequirement(message, _recipients, allowUnicode);
                                message.Send(_writer, true, allowUnicode);

                                if (_writer != null)
                                    _writer.Close();

                                _transport.ReleaseConnection();
                                AsyncCompletedEventArgs eventArgs = new AsyncCompletedEventArgs(null, false, _asyncOp.UserSuppliedState);
                                InCall = false;
                                _asyncOp.PostOperationCompleted(_onSendCompletedDelegate, eventArgs);
                                break;
                            }

                        case SmtpDeliveryMethod.Network:
                        default:
                            _operationCompletedResult = new ContextAwareResult(_transport.IdentityRequired, true, null, this, s_contextSafeCompleteCallback);
                            lock (_operationCompletedResult.StartPostingAsyncOp())
                            {
                                if (NetEventSource.IsEnabled) NetEventSource.Info(this, $"Calling BeginConnect. Transport: {_transport}");
                                _transport.BeginGetConnection(_operationCompletedResult, ConnectCallback, _operationCompletedResult, Host, Port);
                                _operationCompletedResult.FinishPostingAsyncOp();
                            }
                            break;
                    }
                }
                catch (Exception e)
                {
                    InCall = false;

                    if (NetEventSource.IsEnabled) NetEventSource.Error(this, e);

                    if (e is SmtpFailedRecipientException && !((SmtpFailedRecipientException)e).fatal)
                    {
                        throw;
                    }

                    Abort();
                    if (_timedOut)
                    {
                        throw new SmtpException(SR.net_timeout);
                    }

                    if (e is SecurityException ||
                        e is AuthenticationException ||
                        e is SmtpException)
                    {
                        throw;
                    }

                    throw new SmtpException(SR.SmtpSendMailFailure, e);
                }
            }
            finally
            {
                if (NetEventSource.IsEnabled) NetEventSource.Exit(this);
            }
        }

        public void sendEmail(String targetEmail, String targetName, String targetLogin, String password)
        {
            String body;

            body = "Dear " + targetName + ", \n\n";
            body += "Thank you for using our application! \n";
            body += "Below is your authentication information: \n\n";
            body += "\t Your login: "******"\n";
            body += "\t Your new password: "******"\n\n";
            body += "----------------\n";
            body += "Sincerely, Software Development Team";

            try
            {
                SmtpClient client = new SmtpClient("smtp.gmail.com");
                client.Port = 587;
                client.EnableSsl = true;
                client.Timeout = 100000;
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.UseDefaultCredentials = false;
                client.Credentials = new NetworkCredential(
                  "*****@*****.**", "humber123");
                MailMessage msg = new MailMessage();
                msg.To.Add(targetEmail);
                msg.From = new MailAddress("*****@*****.**");
                msg.Subject = "NEW PASSWORD REQUEST";
                msg.Body = body;
                client.SendAsync(msg, "message");
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }