The server response was 5 7 0 Must issue a STARTTLS command first i16sm1806350pag 18 - gsmtp

Question

I am trying to send mail using gmail  and I am getting an exception that is The SMTP server requires a secure connection or the client was not authenticated  The server response was  5 7 0 Must issue a STARTTLS command first  i16sm1806350pag 18 - gsmtp  code I have written for sending mail is   MailMessage mail   new MailMessage     mail To Add txtEmail Text Trim      mail To Add  Secondry gmail com    mail From   new MailAddress  mysendingmail gmail com    mail Subject    Confirmation of Registration on Job Junction    string Body    Hi  this mail is to test sending mail using Gmail in ASP NET   mail Body   Body  mail IsBodyHtml   true  SmtpClient smtp   new SmtpClient  smtp gmail com   587      smtp Host    smtp gmail com     Or Your SMTP Server Address smtp Credentials   new System Net NetworkCredential  mysendingmail gmail com    password       smtp Port   587    Or your Smtp Email ID and Password smtp UseDefaultCredentials   false     smtp EnableSsl   true  smtp Send mail     Please tell me solutions  I am not getting any solutions for this exception

User · Answer

Note to self   quot Remove UseDefaultCredentials   false quot

User · Answer

Gmail requires you to use a secure connection  This can be set in your web config like this    lt network host  smtp gmail com  enableSsl  true        gt    OR   The SSL should be enable on the webserver as well  Refer following link   Enabling SSL on IIS 7 0

User · Answer

I also got the same error using the code   MailMessage mail   new MailMessage     mail To Add txtEmail Text Trim      mail To Add  Secondry gmail com    mail From   new MailAddress  mysendingmail gmail com    mail Subject    Confirmation of Registration on Job Junction    string Body    Hi  this mail is to test sending mail using Gmail in ASP NET   mail Body   Body  mail IsBodyHtml   true  SmtpClient smtp   new SmtpClient  smtp gmail com   587      smtp Host    smtp gmail com     Or Your SMTP Server Address smtp Credentials   new System Net NetworkCredential  mysendingmail gmail com    password       smtp Port   587    Or your Smtp Email ID and Password smtp UseDefaultCredentials   false     smtp EnableSsl   true  smtp Send mail     But moving 2 lines upward fixed the problem   MailMessage mail   new MailMessage     mail To Add txtEmail Text Trim      mail To Add  Secondry gmail com    mail From   new MailAddress  mysendingmail gmail com    mail Subject    Confirmation of Registration on Job Junction    string Body    Hi  this mail is to test sending mail using Gmail in ASP NET   mail Body   Body  mail IsBodyHtml   true  SmtpClient smtp   new SmtpClient  smtp gmail com   587      smtp Host    smtp gmail com     Or Your SMTP Server Address smtp UseDefaultCredentials   false  smtp EnableSsl   true  smtp Credentials   new System Net NetworkCredential  mysendingmail gmail com    password       smtp Port   587    Or your Smtp Email ID and Password smtp Send mail

User · Answer

If you are passing  like me  all the parameters like port  username  password through a system and you are not allow to modify the code  then you can do that easy change on the web config    lt system net gt     lt mailSettings gt       lt smtp gt         lt network enableSsl  true   gt       lt  smtp gt     lt  mailSettings gt   lt  system net gt

User · Answer

https   www google com settings security lesssecureapps  use this link after log in your gmail account and click turn on Then run your application it will work surely

User · Answer

Loginto your gmail account https   myaccount google com u 4 security-checkup 4     See photo  review all locations Google may have blocked for  unknown  or suspicious activity

User · Answer

i Create new E-mail without any phone number or related E-mail then Turn ON less secure app access that done with me

User · Answer

If you get the error  Unrecognized attribute  enableSsl   when following the advice to add that parameter to your web config  I found that I was able to workaround the error by adding it to my code file instead in this format   SmtpClient smtp   new SmtpClient    smtp EnableSsl   true   try       smtp Send mm     catch  Exception ex        MsgBox  Message not emailed      ex ToString         This is the system net section of my web config    lt system net gt     lt mailSettings gt       lt smtp from   lt from email gt   gt         lt network host  smtp gmail com         port  587         userName   lt your email gt          password   lt your app password gt     gt       lt  smtp gt     lt  mailSettings gt   lt  system net gt

User · Answer

SEND Button logic   string fromaddr    YOURMAILID gmail com   string toaddr   TextBox1 Text   TO ADDRESS HERE string password    YOUR PASSWROD    MailMessage msg   new MailMessage    msg Subject    Username  amp password   msg From   new MailAddress fromaddr   msg Body    Message BODY   msg To Add new MailAddress TextBox1 Text    SmtpClient smtp   new SmtpClient    smtp Host    smtp gmail com   smtp Port   587  smtp UseDefaultCredentials   false  smtp EnableSsl   true  NetworkCredential nc   new NetworkCredential fromaddr password   smtp Credentials   nc  smtp Send msg     This code work 100   If you have antivirus in your system or firewall that restrict sending mails from your system so disable your antivirus and firewall  After this run this code    In this above code TextBox1 Text control is used for TOaddress

User · Answer

this is first  part of program    lt head runat  server  gt       lt title gt  lt  title gt       lt style gt           style4                       margin-left 90px                     style3              margin-left 130px                     style2              color white              margin-left 100px              height 400px              width 450px              text-align left                             style1              height 450px              width 550px              margin-left 450px              margin-top 100px              margin-right 500px              background-color rgba 0 0 0 0 9                     body              margin 0              padding 0                    body              background-image url   stock 50 jpg                background-size cover              background-repeat no-repeat                           lt  style gt   lt  head gt   lt body gt       lt form id  form1  runat  server  gt           lt div gt                lt div class  style1  gt                   lt table class  style2  gt                      lt tr gt                          lt td colspan  2  gt  lt h1 class  style4  gt Sending Email lt  h1 gt  lt  td gt                      lt  tr gt                      lt tr gt                          lt td gt To lt  td gt                          lt td gt  lt asp TextBox ID  txtto  runat  server  Height  20px  Width  250px  placeholder  Abc gmail com  gt  lt  asp TextBox gt  lt asp RequiredFieldValidator ForeColor  Red  runat  server  ErrorMessage  Required  ControlToValidate  txtto  Display  Dynamic  gt  lt  asp RequiredFieldValidator gt  lt asp RegularExpressionValidator runat  server  ForeColor  Red  ControlToValidate  txtto  Display  Dynamic  ErrorMessage  Invalid Email ID  ValidationExpression   w   -     w     w   -   w      w   -   w     gt  lt  asp RegularExpressionValidator gt   lt  td gt                      lt  tr gt                        lt tr gt                          lt td gt From lt  td gt                          lt td gt  lt asp TextBox ID  txtfrom  runat  server  Height  20px  Width  250px  placeholder  xyz gmail com  gt  lt  asp TextBox gt   lt asp RequiredFieldValidator ForeColor  Red  Display  Dynamic  runat  server  ErrorMessage  Required  ControlToValidate  txtfrom  gt  lt  asp RequiredFieldValidator gt                              lt asp RegularExpressionValidator Display  Dynamic  runat  server  ErrorMessage  Invalid Email-ID  ControlToValidate  txtfrom  ForeColor  Red  ValidationExpression   w   -     w     w   -   w      w   -   w     gt  lt  asp RegularExpressionValidator gt                            lt  td gt                      lt  tr gt                        lt tr gt                          lt td gt Subject lt  td gt                          lt td gt  lt asp TextBox ID  txtsubject  runat  server  Height  20px  Width  250px  placeholder  Demonstration on Youtube  gt  lt  asp TextBox gt  lt asp RequiredFieldValidator ForeColor  Red  runat  server  ErrorMessage  Required  ControlToValidate  txtsubject  gt  lt  asp RequiredFieldValidator gt   lt  td gt                      lt  tr gt                        lt tr gt                          lt td gt Body lt  td gt                          lt td gt  lt asp TextBox ID  txtbody  runat  server  Width  250px  TextMode  MultiLine  Rows  5  placeholder  This is the body text  gt  lt  asp TextBox gt  lt asp RequiredFieldValidator ForeColor  Red  runat  server  ErrorMessage  Required  ControlToValidate  txtbody  gt  lt  asp RequiredFieldValidator gt   lt  td gt                      lt  tr gt                        lt tr gt                          lt td colspan  2  gt  lt asp Button CssClass  style3  BackColor  Green  BorderColor  green  ID  send  Text  Send  runat  server  Height  30px   Width  100px  OnClick  send Click   gt  lt  td gt                        lt  tr gt                       lt tr gt                           lt td colspan  2  gt  lt asp Label ID  lblmessage  runat  server  gt  lt  asp Label gt   lt  td gt                       lt  tr gt                  lt  table gt               lt  div gt            lt  div gt       lt  form gt   lt  body gt   lt  html gt      this is second part of program    using System  using System Collections Generic  using System Linq  using System Web  using System Web UI  using System Web UI WebControls  using System Net Mail   namespace WebApplication6       public partial class sendingemail1   System Web UI Page               protected void Page Load object sender  EventArgs e                                protected void send Click object sender  EventArgs e                        try                               MailMessage message   new MailMessage                    message To Add txtto Text                   message Subject   txtsubject Text                  message Body   txtbody Text                  message From   new MailAddress txtfrom Text                   SmtpClient client   new SmtpClient  smtp gmail com   587                   client EnableSsl   true                  client Credentials   new System Net NetworkCredential txtfrom Text   Sunil 123                    for int i 1 i lt  100 i                                       client Send message                   lblmessage Text    Mail Successfully send                                               catch  Exception ex                                lblmessage Text   ex Message

User · Answer

This issue haunted me overnight as well  Here s how to fix it    Set host to  smtp gmail com Set port to  587   This is the TLS Port  I had been using all of the other SMTP ports with no success  If you set enableSsl   true like this   Dim SMTP As New SmtpClient HOST  SMTP EnableSsl   True   Trim the username and password fields  good way to prevent errors if user inputs the email and password upon registering like mine does  like this   SMTP Credentials   New System Net NetworkCredential EmailFrom Trim    EmailFromPassword Trim      Using the TLS Port will treat your SMTP as SMTPS allowing you to authenticate  I immediately got a warning from Google saying that my email was blocking an app that has security risks or is outdated  I proceeded to  Turn on less secure apps   Then I updated the information about my phone number and google sent me a verification code via text  I entered it and voila   I ran the application again and it was successful  I know this thread is old  but I scoured the net reading all the exceptions it was throwing and adding MsgBoxes after every line to see what went wrong  Here s my working code modified for readability as all of my variables are coming from MySQL Database   Try     Dim MySubject As String    Email Subject Line      Dim MyMessageBody As String    This is the email body       Dim RecipientEmail As String    recipient gmail com      Dim SenderEmail As String    sender gmail com      Dim SenderDisplayName As String    FirstName LastName      Dim SenderEmailPassword As String    SenderPassword4Gmail       Dim HOST    smtp gmail com      Dim PORT    587   TLS Port      Dim mail As New MailMessage     mail Subject   MySubject     mail Body   MyMessageBody     mail To Add RecipientEmail       mail From   New MailAddress SenderEmail  SenderDisplayName       Dim SMTP As New SmtpClient HOST      SMTP EnableSsl   True     SMTP Credentials   New System Net NetworkCredential SenderEmail Trim    SenderEmailPassword Trim        SMTP DeliveryMethod   SmtpDeliveryMethod Network      SMTP Port   PORT     SMTP Send mail      MsgBox  Sent Message To      amp  RecipientEmail  MsgBoxStyle Information   Sent    Catch ex As Exception     MsgBox ex ToString  End Try   I hope this code helps the OP  but also anyone like me arriving to the party late  Enjoy

User · Answer

Step  1   smtp EnableSsl   true   if not enough   Step  2    Access for less secure apps  must be enabled for the Gmail account used by the NetworkCredential using google s settings page

[c#] The server response was: 5.7.0 Must issue a STARTTLS command first. i16sm1806350pag.18 - gsmtp

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