System.Net.Mail The requested service provider could not be loaded or initialized

Question

I got the following exception when trying to send email using System.Net.Mail.SmtpClient:

System.Net.Mail.SmtpException: The SMTP host was not found.

Inner exception:

System.Net.Sockets.SocketException: The requested service provider could not be loaded or initialized

My email sending code is rather simple:

private async Task SendEmail(string to, string subject, string email)
{
    MailMessage msg = null;
    SmtpClient smtp = null;
    try
    {
        var set = Settings.Default;
        msg = new MailMessage(set.EmailFrom, to, subject, email);
        smtp = new SmtpClient(set.SMTPServer, set.Port)
        {
            EnableSsl = true,
            Credentials = new NetworkCredential(set.EmailUsername, set.EmailPassword),
            Timeout = 20000
        };
        await smtp.SendMailAsync(msg);
    }
    catch (Exception e)
    {
        _log.Error("Error on sending email", e);
        throw;
    }
    finally
    {
        if (msg != null) msg.Dispose();
        if (smtp != null) smtp.Dispose();
    }
}

This error does not happen each time, but rather often. I tried to google it but have not found anything useful. The internet connection seems to be stable when I get this error.

Any ideas why this could happen?

Answer 1

Apologies for not posting this as a comment, I don't have sufficient rep.

I run a process using a very similar implementation to that and I have had the same thing happen to me. Try reducing SMTP the timeout, a new connection will be refused if there are too many requests that haven't let go of their existing connection yet. It's helped with my specific implementation.