C# Mail SMTP Client: Send Message async. Singleton.

MailSmtpClient.cs

using Leaf.Core.Extensions.Net;
//using Leaf.Core.Patterns;

public class MailClient // : Singleton<MailClient>
{
    public static async Task SendAsync(string body, string subject = "Test Email")
    {
        SmtpClient client = null;
        MailMessage mail = null;

        try
        {
            client = new SmtpClient {
                EnableSsl = Config.Smtp.Secure,
                Port = Config.Smtp.Port, // 465 обычно, но для mail ru надо использовать 25, ибо это mail.ru
                DeliveryMethod = SmtpDeliveryMethod.Network,
                UseDefaultCredentials = false,
                Host = Config.Smtp.Server,
                Timeout = 7 * 1000,
                Credentials = new NetworkCredential(Config.Smtp.Email, Config.Smtp.Password)
            };

            mail = new MailMessage(Config.Smtp.Email, Config.Smtp.EmailTo) {
                Subject = subject,
                Body = body
            };

            await client.SendMailAsync(mail, MainUI.Instance.CancelToken);
        }
        finally
        {
            client?.Dispose();
            mail?.Dispose();
        }
    }
}