Unable to read data from the transport connection: net_io_connectionclosed.

Use port 587 with SSL/TLS. Port 465 was never an official secure SMTP port and is functionally depreciated.

For more background, see: Which SMTP Port Should I Use? Understanding Ports 25, 465, & 587

TLS is the successor protocol to SSL. The last version of SSL was depreciated around a decade ago. People still use the term to mean "TLS" though. Anywhere you see "Use SSL" (or similar) in Laserfiche really means "Use TLS".

replied on February 28, 2020

Oh! This whole time I have been staying away from TLS connections because it only has the SSL checkbox. Good to know we can use both. I will have to start another post then for a different error. I have tried connecting to this SMTP server over all possibilities but none work.

Microsoft Dynamics NAV Forum

The SMTP mail system returned the following error: "Failure sending mail. Unable to read data from the transport connection: net_io_connectionclosed

Microsoft Dynamics NAV
---------------------------

The SMTP mail system returned the following error: "Failure sending mail.
Unable to read data from the transport connection: net_io_connectionclosed.".
---------------------------
OK
---------------------------

We are getting this while using office 356 email, gmail with enable of less secure apps and custom domian. non of them is working. Can anyonce help us in that issue how to fix it.

Gearóid responded on 24 Feb 2022 6:08 AM

The SMTP mail system returned the following error: "Failure sending mail. Unable to read data from the transport connection: net_io_connectionclosed

Hi Neha,

This may be caused by not having TLS 1.2 enabled for your NAV 2016 environment. You can enable it by adding the following key to the relevant CustomSettings.config file for the NAV Service:

<add key="SecurityProtocol" value="Tls12" />

You need to have cumulative update 31 (or a later CU) for NAV 2016  to use the above option. See following KB article for more details: https://support.microsoft.com/en-gb/help/4171918

Gearóid responded on 24 Feb 2022 6:08 AM

The SMTP mail system returned the following error: "Failure sending mail. Unable to read data from the transport connection: net_io_connectionclosed

Hi Neha,

This may be caused by not having TLS 1.2 enabled for your NAV 2016 environment. You can enable it by adding the following key to the relevant CustomSettings.config file for the NAV Service:

<add key="SecurityProtocol" value="Tls12" />

You need to have cumulative update 31 (or a later CU) for NAV 2016  to use the above option. See following KB article for more details: https://support.microsoft.com/en-gb/help/4171918

I am trying to send email by using ASP.NET C# code. My website is hosted in godaddy server. It gives this error: Unable to read data from the transport connection: net_io_connectionclosed.

using System.Net.Mail;
using MailMessage = System.Net.Mail.MailMessage;

protected void but_forgot_Click(object sender, EventArgs e)
{
MailMessage mail = new MailMessage();
mail.To.Add(txt_email.Text);
mail.From = new MailAddress("");
mail.Subject = "Recovery Mail";
mail.Body = "Hello " + name + ", your recovery password is given below:" + "\n\nEmail: " + email + "\n\nPassword: " + password;
SmtpClient smtp = new SmtpClient();
smtp.Host = "smtpout.asia.secureserver.net";
smtp.Credentials = new System.Net.NetworkCredential("", "password");
smtp.EnableSsl = false;
smtp.Port = 25;
smtp.Send(mail);
}

Refer -
Cannot get email to work with GoDaddy email SMTP[^]. Implement this.

Quote:

Symptoms

Using GoDaddy SMTP server smptout.secureserver.net email errors occur such as: Mail Error occurred - Exception=Failure sending mail. Unable to read data from the transport connection: net_io_connectionclosed.
Cause

GoDaddy is blocking email relay from most 3rd party hosting providers.
Solution

Use the following SMTP settings for the GoDaddy email server:

Mail Server DNS = relay-hosting.secureserver.net
Mail Server TCP Port = 25

If this won't work, I guess you have to check with the GoDaddy Support team.

Try This..

SmtpClient LocalClient = new SmtpClient();
            MailMessage Mail = new MailMessage();
            Mail.To.Add("ToEmail");
            Mail.From = new MailAddress("fromEmail");
            Mail.Body = "Test Message";
            Mail.Subject = "Mail Local";
          
           
            LocalClient.DeliveryMethod = SmtpDeliveryMethod.PickupDirectoryFromIis;
            LocalClient.Credentials = new NetworkCredential("fromEmail", "Password");
            LocalClient.Send(Mail);

its a framework issue, moving your project to framework 4.6 will resolve the issue.

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