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    lt appSettings gt       lt add key  webpages Version  value  2 0 0 0    gt       lt add key  webpages Enabled  value  false    gt       lt add key  PreserveLoginUrl  value  true    gt       lt add key  ClientValidationEnabled  value  true    gt       lt add key  UnobtrusiveJavaScriptEnabled  value  true    gt          lt add key  smtpServer  value  smtp gmail com    gt       lt add key  EnableSsl  value    true   gt       lt add key  smtpPort  value  587    gt       lt add key  smtpUser  value  sender gmail com    gt       lt add key  smtpPass  value  mypassword    gt       lt add key  adminEmail  value  sender gmail com    gt     lt  appSettings gt     lt system net gt       lt mailSettings gt         lt smtp from  sender gmail com  gt           lt network host  smtp gmail com  password  mypassword  port  587  userName  sender gmail com   enableSsl  true   gt         lt  smtp gt       lt  mailSettings gt     lt  system net gt    what should i do to solve this error and send mail

User · Answer

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.

User · Answer

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

User · Answer

Make sure that Access less secure app is allowed           MailMessage mail   new MailMessage            mail From   new MailAddress  xx gmail com            mail Sender   new MailAddress  xx gmail com            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  xx gmail com    xx            smtp DeliveryMethod   SmtpDeliveryMethod Network          smtp EnableSsl   true           smtp Timeout   30000          try                        smtp Send mail                     catch  SmtpException e                        textBox1 Text  e Message

User · Answer

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  to-mail gmail com    test    Hi it worked          from-mail    from-username    from-password    smtp   587

User · Answer

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   lt system net gt               lt mailSettings gt                   lt smtp deliveryMethod  Network  from  admin example com  gt                       lt network defaultCredentials  false  host  smtp example com  port  25  userName  admin example com  password  password   gt                   lt  smtp gt               lt  mailSettings gt           lt  system net gt

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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 gmail com        mail To Add  somebody domain com        mail Subject    Hello World       mail Body     lt h1 gt Hello lt  h1 gt        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 gmail com    password            smtp EnableSsl   true          smtp Send mail             ------------------- Info shared by Michael Freidgeim in below comments area  Similar answer with screenshots https   stackoverflow com a 32457468 52277

User · Answer

I ve searched and tried different things for hours   To summarize  I had to take into consideration the following points    Use smtp gmail com instead of smtp google com Use port 587 Set client UseDefaultCredentials   false  before setting credentials Turn on the Access for less secure apps 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

User · Answer

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- gt click on see all settings- gt Forwarding  and IMAP POP- gt check pop and imap is enabled  if not enable it- gt Save  changes  step2-click on your gmail profile picture- gt click on Manage your google account- gt go to security tab- gt check for Access to less secure apps this option will be available if you havent opt for two step verification - gt 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- gt click on Manage your google account- gt go to security tab- gt search for  APP PASSWORD- gt select any app name given- gt select any device name- gt click on  generate- gt 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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

Try it this way  I just made some light changes   MailMessage msg   new MailMessage     msg From   new MailAddress  mymailid gmail com    msg To Add  receipientid gmail com    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  mymailid gmail com    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

User · Answer

After turning less secure option on and trying other solutions  if you are still facing the same problem try to use this overload   client Credentials   new NetworkCredential  mymailid    mypassword      instead of   client Credentials   new NetworkCredential  mymailid    mypassword    smtp gmail com

User · Answer

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  fromaddress gmail com                mail To Add  toaddress1 gmail com                mail To Add  toaddress2 gmail com                mail Subject    Password Recovery                mail Body       lt html gt                mail Body      lt body gt                mail Body      lt table gt                 mail Body      lt tr gt                mail Body      lt td gt User Name    lt  td gt  lt td gt  HAi  lt  td gt                mail Body      lt  tr gt                 mail Body      lt tr gt                mail Body      lt td gt Password    lt  td gt  lt td gt aaaaaaaaaa lt  td gt                mail Body      lt  tr gt                 mail Body      lt  table gt                mail Body      lt  body gt                mail Body      lt  html gt                 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

User · Answer

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

User · Answer

Turn on less secure app from this link and boom

User · Answer

App Passwords helped me   Go to https   myaccount google com security  Scroll down to  quot Signing in to Google quot   Enable 2-Step Verification  Add App Password  Use the generated password in your code

User · Answer

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   docs microsoft com en-us exchange clients-and-mobile-in-exchange-online authenticated-client-smtp-submission

User · Answer

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

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

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