ASP.Net Core Site Stops Sending Emails Citing Mysterious SSL Issue

PostAlmostAnything 1

What might suddenly make it impossible for a .Net 5 website to stop sending email citing the following:

An unhandled exception occurred while processing the request.
InvalidOperationException: An error occurred while attempting to establish an SSL or TLS connection.

The server's SSL certificate could not be validated for the following reasons:
• The server certificate has the following errors:
• A required certificate is not within its validity period when verifying against the current system clock or the timestamp in the signed file.
MySite.Pages.contact.IndexModel.SendEmailAdmin(string name, string email, string subject, string message) in Index.cshtml.cs, line 143

Rebin Qadir 151 Reputation points

2022-05-14T08:36:59.247+00:00

Could you please share the code with us !
PostAlmostAnything 1 Reputation point

2022-05-14T18:00:12.537+00:00
Sure, but I've since noticed that the AutoSSL feature of the mail server is issuing certificates that expire in a matter of hours. I think that is probably the problem since every other cPanel account that hosts mail for sites physically hosted on the same Windows server as this one don't have the problem. I would like to know if I am on the right track and need to move my inquiry to the cPanel site.

Is there a way to tell .Net to send emails no matter what even if the SSL certificate is technically expired?

My code includes the following which has ALWAYS worked fine:

using (SmtpClient client = new SmtpClient()) { await client.ConnectAsync("mail.example.com", 587, useSsl: false); await client.AuthenticateAsync("noreply@example.com", "mypw"); await client.SendAsync(msg); await client.DisconnectAsync(quit: true); }
PostAlmostAnything 1 Reputation point

2022-05-14T18:18:02.48+00:00

Also, I still think that despite the expired cert this is a problem with .Net Core because I can still use Outlook to send/receive emails from that server despite the expired cert. This indicates that somebody built something into .Net which won't allow it to send mail to servers with expired certs.

Again, can you force .Net to send messages anyway or disable the SSL check?
Bruce (SqlWork.com) 55,601 Reputation points

2022-05-14T18:28:23.207+00:00
it is the SmtpClient that needs to support invalid certificates. it is also not recommended to use. if your hosting O/S supports, you can

ServicePointManager.ServerCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) => true;

to disable all ssl verification.

Rebin Qadir 151

Try to ignore certificate errors as @Alexander Nulens | Finvision-Brussels mentioned in the comment.

   ServicePointManager.ServerCertificateValidationCallback = errorCertHandler;  
      
    private bool errorCertHandler(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors error)  
          
       {  
      
            return true;  
       }

PostAlmostAnything 1 Reputation point

2022-05-15T02:35:46.797+00:00

That words on my local machine, thanks. However, I am more confused now because the AutoSSL appears to be working fine and the expiration date is not until August now, so I know that can't be it. I was hoping the valid certificate would solve the rest.