smtp requires the client not authenticaed

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now the SMTP server requires a secure connection or the client was not authenticated to the server response was: 5.51 Client was not authenticated

Posted 2-Apr-13 21:43pm

msashwin03

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Westlmorland 21-Mar-17 8:12am

Try this:

using (SmtpClient smtp = new SmtpClient(" (e.g. smtp.gmail.com)", ConnectionSecurity.Ssl, true))
{
smtp.Connect();
Console.WriteLine("Connected.");

smtp.Authenticate("<username>", "<password>");
Console.WriteLine("Authenticated.");

// ...
}

The code uses this smtp client for c#.
Also here is a complete example on how you can send email in asp.net application with c# or vb.net.

3 solutions

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Thomas Daniels · Answer 1 · 2013-04-02T21:50:00

Solution 1

Hi,

Try to set the SmtpClient.EnableSsl[^] property to true:

C#

yourSmtpClient.EnableSsl = true; // change 'yourSmtpClient' into the name of your SmtpClient

Hope this helps.

Posted 2-Apr-13 21:50pm

Thomas Daniels

_Amy · Answer 2 · 2013-04-02T22:22:00

Try setting EnableSSL to true for your SMTP Client.

C#

smtpClient.EnableSsl = true;

Check a Tip here:
Tip/Trick: Enabling SSL on IIS 7.0 Using Self-Signed Certificates[^]

Or refer the links below for Similar Threads:
http://forums.asp.net/p/1156294/1899489.aspx#1899489[^]
http://forums.asp.net/p/1144253/1848821.aspx#1848821[^]
http://forums.asp.net/p/1117050/1736785.aspx#1736785[^]

--Amit

Anuja Pawar Indore · Answer 3 · 2013-04-02T23:51:00

Solution 3

Try these similar threads.
http://stackoverflow.com/questions/10698779/the-smtp-server-requires-a-secure-connection-or-the-client-was-not-authenticated[^]

http://stackoverflow.com/questions/6477055/the-smtp-server-requires-a-secure-connection-or-the-client-was-not-authenticated[^]

Posted 2-Apr-13 23:51pm

Anuja Pawar Indore