The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required?

Question

I want to send an email from my application and i have written following code for sending mail

    MailMessage msg = new MailMessage();

    msg.From = new MailAddress("mymailid");
    msg.To.Add("receipientid");
    msg.Subject = "test";
    msg.Body = "Test Content";
    msg.Priority = MailPriority.High;

    SmtpClient client = new SmtpClient();

    client.Credentials = new NetworkCredential("mymailid", "mypassword", "smtp.gmail.com");
    client.Host = "smtp.gmail.com";
    client.Port = 587;
    client.DeliveryMethod = SmtpDeliveryMethod.Network;
    client.EnableSsl = true;
    client.UseDefaultCredentials = true;

    client.Send(msg);

I am running it on localhost so what mistake i am doing to send it.

When i send button it gives an error like

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

Code in Web.config file

 <appSettings>
    <add key="webpages:Version" value="2.0.0.0" />
    <add key="webpages:Enabled" value="false" />
    <add key="PreserveLoginUrl" value="true" />
    <add key="ClientValidationEnabled" value="true" />
    <add key="UnobtrusiveJavaScriptEnabled" value="true" />   
    <add key="smtpServer" value="smtp.gmail.com" />
    <add key="EnableSsl" value = "true"/>
    <add key="smtpPort" value="587" />
    <add key="smtpUser" value="[email protected]" />
    <add key="smtpPass" value="mypassword" />
    <add key="adminEmail" value="[email protected]" />
  </appSettings>
  <system.net>
    <mailSettings>
      <smtp from="[email protected]">
        <network host="smtp.gmail.com" password="mypassword" port="587" userName="[email protected]"  enableSsl="true"/>
      </smtp>
    </mailSettings>
  </system.net>

what should i do to solve this error and send mail??

Pickup

possible duplicate of Sending email in .NET through Gmail – Duffer

I think you may have to look in to this answer, too : https://mcmap.net/q/22204/-sending-email-through-gmail-smtp-server-with-c – Whyte

I had the same problem. check [this post][1] [1]: https://mcmap.net/q/144320/-the-smtp-server-requires-a-secure-connection-or-the-client-was-not-authenticated-if-uploading-on-godaddy – Bullard

You should consider to specify SMTP configuration data in config file and do not overwrite them in a code - see SMTP configuration data at systemnetmail.com/faq/4.1.aspx – Counterpart

it's may help you The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.1 Client was not authenticated – Irfan

Update 6/30/2020: With port 587 and EnableSsl = TRUE and Google less secure ON it should works. ALSO ENABLE SSL/TLS support on your host (in your website control panel); For example in Plesk control panel, Add a self-signed SSL/TLS Certificate, then go to Hosting Settings and enable that damn SSL/TLS checkbox. – Clitoris

Answer 1

First check for gmail's security related issues. You may have enabled double authentication in gmail. Also check your gmail inbox if you are getting any security alerts. In such cases check other answer of @mjb as below

Below is the very general thing that i always check first for such issues

client.UseDefaultCredentials = true;

set it to false.

Note @Joe King's answer - you must set client.UseDefaultCredentials before you set client.Credentials

Abran

In that case you should share your code. Above answer is for the code in question – Abran

Note @Joe King's answer - you must set client.UseDefaultCredentials before you set client.Credentials – Nix

This answer won't work, I think most people faced security on gmail side. see mjb's answer for a proper solution – Geneviegenevieve

Also, make sure the "Captcha" is disabled - this may be necessary if you are running the script on a remote server (not necessary when running on local machine): accounts.google.com/DisplayUnlockCaptcha – Delldella

Setting client.UseDefaultCredentials = false; before client.Credentials and setting client.EnableSsl = true; did the trick in my case. – Gurley

I had the same problem, it worked after I "Turn on" access to less secure app via gmail alerts – Georgiageorgian

Nops, doesnt work for me either. I have set it to false before the credentials, just after creating the SmtpClient object, no difference. THe docs also says that this is set to false by default, so I guess it was false from the beginning for me. – Whirly

@SaadA said it: Its google who blocked the usage/login. It said it had blocked login attempts, and that I should enable "less secure apps". Which I did, and then it works. – Whirly

Super duper duper duper duper duper dooper thank you. I had been haggling with this for all of today since morning (over 7 hours now) trying out "App Passwords", "Less Secure Accounts" turning them off and on, and a whole lot of other things. Turns out just setting the client.UseDefaultCredentials = false before setting the client.Credentials made it work. That was all that the problem was. Holy phew now! – Elrod

First I turned off gmail two step verification. and Allow Less secure app access: ON.. worked for me. – Lafrance

As of May 30, 2022 less secure apps are no longer supported from Googlem so you have to use App Passwords. support.google.com/accounts/answer/… – Dutchman

Answer 2

I have the same problem.

I have found this solution:

Google may block sign in attempts from some apps or devices that do not use modern security standards. Since these apps and devices are easier to break into, blocking them helps keep your account safer.

Some examples of apps that do not support the latest security standards include:

• The Mail app on your iPhone or iPad with iOS 6 or below
  
• The Mail app on your Windows phone preceding the 8.1 release
  
• Some Desktop mail clients like Microsoft Outlook and Mozilla Thunderbird

Therefore, you have to enable Less Secure Sign-In (or Less secure app access) in your google account.

After sign into google account, go to:

https://www.google.com/settings/security/lesssecureapps
or
https://myaccount.google.com/lesssecureapps

In C#, you can use the following code:

using (MailMessage mail = new MailMessage())
{
    mail.From = new MailAddress("[email protected]");
    mail.To.Add("[email protected]");
    mail.Subject = "Hello World";
    mail.Body = "<h1>Hello</h1>";
    mail.IsBodyHtml = true;
    mail.Attachments.Add(new Attachment("C:\\file.zip"));

    using (SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587))
    {
        smtp.Credentials = new NetworkCredential("[email protected]", "password");
        smtp.EnableSsl = true;
        smtp.Send(mail);
    }
}

Sharpshooter

This along with ensuring that SSL was enabled in the code has worked wonders, thanks a lot – Suburban

this should be the selected answer – Jamaaljamaica

This was my issue, thank you for going through the trouble and giving out a more explanatory answer. – Vociferate

Yep. Turns out I had to enable "Less Secure Sign-In" on my target gmail account. Thanks! – Lucinalucinda

I have turned on "access for less secure apps" - yet it still fails (and logs the failure on the gmail site). Any ideas how I can force it to work? – Clein

Also, make sure the google "Captcha" is disabled - this may be necessary if you are running the script on a remote server (not necessary when running on local machine): accounts.google.com/DisplayUnlockCaptcha – Delldella

@MichaelFreidgeim thanks for the sharing, I have added your info into my post – Sharpshooter

Da, this solves my problem. :). Thank you for sharing. – Sloth

Awesome...... You saved my time. And thanks a ton for the direct link to turn off the switch! – Linnlinnaeus

This should be the ANSWER. – Solfeggio

best answer ta. It all comes down to the google less secure sign in, nothing to do with code on the developer side. – Clausewitz

I turned it on before. but it was switched to off again after a while. I turned it on again and it works. thanks. – Consubstantiate

Less secure app enabling feature is no longer available in google account for security reasons! Using App Password resolved the problem! As answered by @Roman O https://mcmap.net/q/142076/-the-smtp-server-requires-a-secure-connection-or-the-client-was-not-authenticated-the-server-response-was-5-5-1-authentication-required – Submerse

As of May 30, 2022 less secure apps are no longer supported from Googlem so you have to use App Passwords. support.google.com/accounts/answer/… – Dutchman

solution for gmail is here #67950793 – Genetic

Answer 3

Ensure you set SmtpClient.Credentials after calling SmtpClient.UseDefaultCredentials = false.

The order is important as setting SmtpClient.UseDefaultCredentials = false will reset SmtpClient.Credentials to null.

Lesh

I've been looking for the solution to this for half an hour, yours is the only little post on the internet I've found that mentions the ordering of this. Thanks mate. – Whitesell

@Joe King You are just awesome mate..... was searching for this since 3 hours :) – Guarantor

Thank you @Joe King that is vital information missing from the MS docs. This was the solution to my problem sending with username and password also. – Nix

This is easily overlooked but the ordering is important as I just found out. – Patency

yeah. saved my day. you need to call UseDefaultCredentials = false before setting Credentials. – Joline

That is a lifesaving answer! Thanks! – Indecorum

I spent days looking for this answer. note that the order also makes a difference if your smtp client settings are in the web.config. for example: <network defaultCredentials="false" host="smtp.office365.com" port="587" enableSsl="true" userName="[email protected]" password="pwd" /> – Individuate

Answer 4

I've searched and tried different things for hours.. To summarize, I had to take into consideration the following points:

1. Use smtp.gmail.com instead of smtp.google.com
2. Use port 587
3. Set client.UseDefaultCredentials = false; before setting credentials
4. Turn on the Access for less secure apps
5. Set client.EnableSsl = true;

If these steps didn't help, check this answer.
Perhaps, you can find something useful on this System.Net.Mail FAQ too.

Gurley

This answer is very useful... solved my problem. Thanks a lot – Soho

if it's still not working, go on this link g.co/allowaccess and allow access – Retene

"Access for less secure apps" saved my day. – Mcclung

This part did it for me: "Turn on the Access for less secure apps". Thanks! – Helio

Access for less secure apps take care may be you logged in by two accounts and you changed it on differenent one – Reseau

Answer 5

App Passwords helped me.

1. Go to https://myaccount.google.com/security.
2. Scroll down to "How you sign in to Google".
3. Enable 2-Step Verification.
4. Add App Password.
5. Use the generated password in your code.

You can also use direct link https://myaccount.google.com/apppasswords

Convexoconcave

Although this solution works, it would send emails right into the Spam folder. Please, double-check this. Thanks. – Accurate

after 30th May 2022 with removal of less secure option, App Password is working, you'll have to set two step verification first then you can generate app password and use it in your code – Dysgraphia

@Dysgraphia despite doing both, my program isnt working. Please help. – Seismography

A wonderful solution considering security risks. – Stokehole

Answer 6

As of May 30, 2022 less secure apps are no longer supported from Google so you have to use App Passwords.

https://support.google.com/accounts/answer/6010255?authuser=1&hl=en-GB&authuser=1&visit_id=637957424028050444-425688120&p=less-secure-apps&rd=1

Here are the steps to set up an app password via google: https://support.google.com/accounts/answer/185833?authuser=1

Then you need to use the 16 character app password for the smtpClient's credentials:

smtpClient = new SmtpClient(emailHost)
{
     Port = port,
     DeliveryMethod = SmtpDeliveryMethod.Network,
     Credentials = new NetworkCredential(fromEmail, emailPassword),
     EnableSsl = true,
 };

The emailpassword should be the 16 character generated App Password.

Port: 587

Emailhost: smtp.gmail.com

Then the rest of the code:

var mailMessage = new MailMessage{
                    From = new MailAddress(fromEmail),
                    Subject = "Yoursubject",
                    Body = $"Your body",
                    IsBodyHtml = true,
                };
                mailMessage.To.Add(newEmail);

                if (smtpClient != null)
                    smtpClient.Send(mailMessage);

Dutchman

This answer really helped me, except for emailhost which was bit confusing due to upper and lowercase – Crowboot

Answer 7

Try it this way, I just made some light changes:

MailMessage msg = new MailMessage();

msg.From = new MailAddress("[email protected]");
msg.To.Add("[email protected]");
msg.Subject = "test";
msg.Body = "Test Content";
//msg.Priority = MailPriority.High;


using (SmtpClient client = new SmtpClient())
{
    client.EnableSsl = true;
    client.UseDefaultCredentials = false;
    client.Credentials = new NetworkCredential("[email protected]", "mypassword");
    client.Host = "smtp.gmail.com";
    client.Port = 587;
    client.DeliveryMethod = SmtpDeliveryMethod.Network;

    client.Send(msg);
}

Also please show your app.config file, if you have mail settings there.

Pitcher

I have not yet configured in it. what should i write there? – Pickup

there is no app.config file in my mvc application. – Pickup

I tried many other solution, but only this one worked. Thanks – Kurtzman

Answer 8

Try to login in your gmail account. it gets locked if you send emails by using gmail SMTP. I don't know the limit of emails you can send before it gets locked but if you login one time then it works again from code. make sure your webconfig setting are good.

Bombacaceous

Best answer indeed! I logged in again and it worked ! PS: I had to provide a captcha on Google – Simonne

I got this error as my Google account is protected with two-factor authentication. I ended up creating a dedicated account to send the email from. – Busra

Answer 9

Turn on less secure app from this link and boom...

Petrography

This worked for me .. This must be the accepted answer – Bannister

Answer 10

try to enable allow less secure app access.

Here, you can enable less secure app after login with your Gmail.

https://myaccount.google.com/lesssecureapps

Thanks.

Cherlycherlyn

Answer 11

For security reasons, Google has discontinued turning on Access for Less Secure Apps, effective from May 30, 2021. Hence, some of the answers here that emphasized enabling access for less secure apps have become obsolete.

Here is an answer I found on VB Forum and it worked for me. I was able to send a mail successfully.

"Please do following steps. In Google Account Activate 2-step verification. Select App Password in Google Account => Security => Signing to Google. In Select App Combo Select Other and Name as Windows App & Click Generate it. Copy Password and use it in place of email password. It will work."

Check out the link to see more answers. https://www.vbforums.com/showthread.php?895413-Sending-Email-via-Gmail-changing-for-May-30

Scroll down and see the answer posted by microbrain

See the code with which I sent my mail below:

Dim emailTo As String = TxtEmail.Text.Trim()
        If emailTo.Length > 10 Then
            Try
                Dim Smtp_Server As New SmtpClient
                Dim e_mail As New MailMessage()
                Smtp_Server.UseDefaultCredentials = False
                Smtp_Server.Credentials = New Net.NetworkCredential("[email protected]", "***16-digit-code***")
                Smtp_Server.Port = 587
                Smtp_Server.EnableSsl = True
                Smtp_Server.Host = "smtp.gmail.com"

                e_mail = New MailMessage()
                e_mail.From = New MailAddress("[email protected]")
                e_mail.To.Add(emailTo)
                e_mail.Subject = "Login OTP"
                e_mail.IsBodyHtml = False
                e_mail.Body = "some text here"
                Smtp_Server.Send(e_mail)
                MessageBox.Show("Your login OTP has been sent to " & emailTo)
                LblOTPSuccess.Visible = True
                TxtOTP.Visible = True
                BtnVerifyOTP.Visible = True
                TxtOTP.Focus()
            Catch error_t As Exception
                MessageBox.Show(error_t.ToString, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
            End Try
        Else
            MessageBox.Show("Email address is invalid or too short", "Invalid Email", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End If

Remember to change the parameters in the code to suit you.

Throw

Answer 12

I encountered the same problem even I set "UseDefaultCredentials" to false. Later I found that the root cause is that I turned on "2-step Verification" in my account. After I turned it off, the problem is gone.

Annabal

Don't turn off 2 step verification. It s there for a reason. You can generate an application-specific password in GMail settings and use that in the SmtpClient. You should be doing that regardless rather than exposing a normal password. – Cork

Answer 13

Make sure that Access less secure app is allowed.

        MailMessage mail = new MailMessage();
        mail.From = new MailAddress("[email protected]");
        mail.Sender = new MailAddress("[email protected]");
        mail.To.Add("external@emailaddress");
        mail.IsBodyHtml = true;
        mail.Subject = "Email Sent";
        mail.Body = "Body content from";

        SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587);
        smtp.UseDefaultCredentials = false;

        smtp.Credentials = new System.Net.NetworkCredential("[email protected]", "xx");
        smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
        smtp.EnableSsl = true;

        smtp.Timeout = 30000;
        try
        {

            smtp.Send(mail);
        }
        catch (SmtpException e)
        {
            textBox1.Text= e.Message;
        }

Carrol

The link to toggle the setting for "Access less secure app" is here - google.com/settings/security/lesssecureapps Changing the setting didn't help me overcome the error – Ceria

Answer 14

In my case, I was facing the same issue. After a long research, don't set UseDefaultCredentials value to false. Because default value of UseDefaultCredentials is false.

Another key point is to set network credential just before the client.send(message) statement.

Wrong Code:

SmtpClient client = new SmtpClient();
client.Host = ServerName; 
var credentials = new System.Net.NetworkCredential(UserName, Password);
client.Credentials = credentials;
client.Port = Port;
client.EnableSsl = EnableSSL;
client.UseDefaultCredentials = false;
client.Send(message);

Wrong Code:

SmtpClient client = new SmtpClient();
client.Host = ServerName; 
var credentials = new System.Net.NetworkCredential(UserName, Password);
client.Credentials = credentials;
client.Port = Port;
client.EnableSsl = EnableSSL;
client.UseDefaultCredentials = true;
client.Send(message);

Correct code

SmtpClient client = new SmtpClient();
client.Host = ServerName; 
var credentials = new System.Net.NetworkCredential(UserName, Password);
client.Credentials = credentials;
client.Port = Port;
client.EnableSsl = EnableSSL;
// client.UseDefaultCredentials = true;
client.Send(message);

Correct code

SmtpClient client = new SmtpClient();
client.Host = ServerName; 
client.Port = Port;
client.EnableSsl = EnableSSL;
client.UseDefaultCredentials = false;
var credentials = new System.Net.NetworkCredential(UserName, Password);
client.Credentials = credentials;
client.Send(message);

Now its working ok with both corrected codes. So in this case sequence matters.

Cheers!

Engracia

Answer 15

Below is my code.I also had the same error but the problem was that i gave my password wrong.The below code will work perfectly..try it

            MailMessage mail = new MailMessage();
            SmtpClient SmtpServer = new SmtpClient("smtp.gmail.com");              
            mail.From = new MailAddress("[email protected]");
            mail.To.Add("[email protected]");
            mail.To.Add("[email protected]");
            mail.Subject = "Password Recovery ";
            mail.Body += " <html>";
            mail.Body += "<body>";
            mail.Body += "<table>";

            mail.Body += "<tr>";
            mail.Body += "<td>User Name : </td><td> HAi </td>";
            mail.Body += "</tr>";

            mail.Body += "<tr>";
            mail.Body += "<td>Password : </td><td>aaaaaaaaaa</td>";
            mail.Body += "</tr>";

            mail.Body += "</table>";
            mail.Body += "</body>";
            mail.Body += "</html>";

            mail.IsBodyHtml = true;
            SmtpServer.Port = 587;
            SmtpServer.Credentials = new System.Net.NetworkCredential("sendfrommailaddress.com", "password");
            SmtpServer.EnableSsl = true;

            SmtpServer.Send(mail);

You can reffer it in Sending mail

Christogram

Answer 16

If it's a new google account, you have to send an email (the first one) through the regular user interface. After that you can use your application/robot to send messages.

Wittie

Answer 17

You should consider to specify SMTP configuration data in config file and do not overwrite them in a code - see SMTP configuration data at http://www.systemnetmail.com/faq/4.1.aspx

<system.net>
            <mailSettings>
                <smtp deliveryMethod="Network" from="[email protected]">
                    <network defaultCredentials="false" host="smtp.example.com" port="25" userName="[email protected]" password="password"/>
                </smtp>
            </mailSettings>
        </system.net>

Counterpart

Answer 18

I have encountered the same problem several times. After enabling less secure app option the problem resolved. Enable less secure app from here: https://myaccount.google.com/lesssecureapps

hope this will help.

Outburst

Answer 19

I created a Microsoft 365 Developer subscription (E5) today morning and used it to send a test email using the following settings

using (SmtpClient client = new SmtpClient())
{
    client.EnableSsl = true;
    client.UseDefaultCredentials = false;
    client.Credentials = new NetworkCredential(username, password);
    client.Host = "smtp.office365.com";
    client.Port = 587;
    client.DeliveryMethod = SmtpDeliveryMethod.Network;

    client.Send(msg);
}

It did not work in the beginning, as I kept getting this error message with the exception thrown by this code. Then, I spent about 4+ hours playing with the Microsoft 365 admin centre settings and reading articles to figure out the issue. Ultimately I changed my Microsoft 365 admin centre password and it worked like a charm. So, it is worth to try changing the password when you get this message, before thinking about any advance solution.

Note that the password wasn't invalid for sure as I logged on to my Microsoft 365 account without any issues. however, the password change solved the issue.

Iredale

Answer 20

After going through each of every proposed solution, I realized the correct answer depends on your current server and email client situation. In my case, I have the MX record pointing to my on-premise outbound server. Also, since I'm using G Suite and not Gmail to send my notification emails, I had to follow this configuration: https://support.google.com/a/answer/2956491?hl=en.

Having said this, I found the right way to make this work, is indeed configuring the SMTP relay service first from my G Suite account:

IPv6 address is the address of the webserver the MX record is pointing at (example: 1234:454:c88a:d8e7:25c0:2a9a:5aa2:104).

Once this is done, use this code to complement the solution:

 //Set email provider credentials
 SmtpClient smtpClient = new SmtpClient("smtp-relay.gmail.com", "587");                   

 smtpClient.EnableSsl = true;
 smtpClient.UseDefaultCredentials = true;
 
 MailAddress from = new MailAddress("[email protected]", "EmailFromAlias");
 MailAddress to = new MailAddress("[email protected]");

 MailMessage = new MailMessage(from, to);

 MailMessage.Subject = subject;
 MyMailMessage.Body = message;

 MyMailMessage.IsBodyHtml = false;

 smtpClient.Send(MyMailMessage);

Please, notice that with this method, smtpClient.UseDefaultCredentials = true; and not false as suggested in other solutions. Also, since we use the IPv6 address to connect to the SMTP client, it's not required to specify the user name or password. Therefore, in my opinion, this is a more secure and safe approach.

Accurate

admin.google.com is used for Google Workspace accounts only. Regular Gmail accounts cannot be used to sign in to admin.google.com – Consubstantiate

Answer 21

some smtp servers (secure ones) requires you to supply both username and email, if its gmail then most chances its the 'Less Secure Sign-In' issue you need to address, otherwise you can try:

public static void SendEmail(string address, string subject, 
    string message, string email, string username, string password, 
    string smtp, int port)
{
    var loginInfo = new NetworkCredential(username, password);
    var msg = new MailMessage();
    var smtpClient = new SmtpClient(smtp, port);

    msg.From = new MailAddress(email);
    msg.To.Add(new MailAddress(address));
    msg.Subject = subject;
    msg.Body = message;
    msg.IsBodyHtml = true;

    smtpClient.EnableSsl = true;
    smtpClient.UseDefaultCredentials = false;
    smtpClient.Credentials = loginInfo;
    smtpClient.Send(msg);
}

notice that the email from and the username are different unlike some implementation that refers to them as the same.

calling this method can be done like so:

SendEmail("[email protected]", "test", "Hi it worked!!", 
   "from-mail", "from-username", "from-password", "smtp", 587);

Enfilade

Answer 22

If you are in a test environment and do not want to set security settings you have to allow less secure apps via. this link in Gmail.

https://myaccount.google.com/lesssecureapps

Hearken

Answer 23

I had the same issue, it was resolved by change password to strong password.

Thousandth

Answer 24

If you face this issue with Office 365 account. In Exchange Online, by default, the SMTP Client Authentication will be disabled for all Office 365 mailbox accounts. You have to manually enable SMTP Auth for the problematic account and check the case again. Check the below threads.

https://morgantechspace.com/2021/01/the-smtp-server-requires-a-secure-connection-or-the-client.html

https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission

Trisect

Answer 25

I have used the steps in this question and it worked for me.

My issue was that G suite didn't consider my password as strong and after changing it it worked perfectly.

Empathize

Answer 26

If all mentioned solutions didn't help, try to use this URL - it helped me to unblock email sending at my website

https://g.co/allowaccess

Untread

Answer 27

that can be if: 1)the user or pass are wrong 2)not enable SSL 3)less secure app is not enable 4)you have not log in into the server with this mail 5)you have not set client.UseDefaultCredentials = false

Crocked

Answer 28

Removing the port field worked in my case

Bernardinebernardo

Answer 29

Although this question is regarding the error" The server response was: 5.5.1 Authentication Required. We are presented with this result when we search for The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required

Hence this answer is for those who are getting an error:

The server response was: 5.7.0 Authentication Required.

If your C# code is correct, change these 2 settings in your Google Account. This error arises mostly when the code is correct, but the account is not set properly to send emails.

• Enable 2 Step verification in Your Google Account.

  • In your account settings click Manage your Google Account.

  • Under Security. You'll find How you sign in to Google section. Enable 2 Step verification by following the process.

• Get App Password from How you sign in to Google section.

Follow this YouTube video for the enabling process.

You can use your own code from official documentation.

Vibraphone

Answer 30

I was also facing the issue like 'The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.0 Authentication Required' then went through so much internet materials but it didn't helped me fully. How I solved it like

step1:smtp.gmail.com is gmail server so go to your account gmail settings->click on see all settings->Forwarding and IMAP/POP->check pop and imap is enabled ,if not enable it->Save changes. step2-click on your gmail profile picture->click on Manage your google account->go to security tab->check for Access to less secure apps(this option will be available if you havent opt for two step verification)->by default google will set it as disable, make it enable to use your real gmail password working for sending email. note:-Enabling gmail access for less secure apps,may be dangerous for you so i dont recommend this

step3:-if your account has two step verification enabled or want to use password other than your gmail Real password using app specific password then try this:- click on your gmail profile picture->click on Manage your google account->go to security tab->search for APP PASSWORD->select any app name given->select any device name->click on generate->copy the 16-digit password and paste it into your app where you have to enter a gmail password in place of your real gmail password.

Familial

Answer 31

Try it this way and nesessarily enable Less secure apps by clicking this link

        var fromEmail = new MailAddress("[email protected]", "Title");
        var toEmail = new MailAddress(emailID);
        var fromEmailPassword = "yourPassword"; 
         

        var smtp = new SmtpClient
        {
            Host = "smtp.gmail.com",
            Port = 587,
            EnableSsl = true,
            DeliveryMethod = SmtpDeliveryMethod.Network,
            UseDefaultCredentials = false,
            Credentials = new NetworkCredential(fromEmail.Address, fromEmailPassword)
        };
            using (var message = new MailMessage(fromEmail, toEmail)
            {
                Subject = subject,
                Body = body,
                IsBodyHtml = true
            })

                smtp.Send(message);

Thoroughgoing