An attempt was made to access a socket in a way forbidden by its access permissions while using SMTP

Question

I am trying to send an SMTP email when certain values in database crosses its threshold value   I have already allowed ports 25 587 and 465 in the Windows firewall and disabled the option of preventing mass mail in the Antivirus  The code I am using is given below  using System Net  using System Net Mail  using System Net Security  using System Security Cryptography X509Certificates    MailMessage mailMsg   new MailMessage            mailMsg To Add  to domain com               From         MailAddress mailAddress   new MailAddress  from domain com            mailMsg From   mailAddress               Subject and Body         mailMsg Subject    MCAS Alert           mailMsg Body    Parameter out of range             SmtpClient smtpClient   new SmtpClient  smtp servername com   25           smtpClient UseDefaultCredentials   false          smtpClient Timeout   30000          System Net NetworkCredential credentials              new System Net NetworkCredential  username    passwrod            smtpClient Credentials   credentials          smtpClient EnableSsl   true            ServicePointManager ServerCertificateValidationCallback   delegate object s  X509Certificate certificate  X509Chain chain  SslPolicyErrors sslPolicyErrors    return true             smtpClient Send mailMsg     Stack Trace   SocketException  0x271d   An attempt was made to access a socket in a way forbidden by its access permissions xx xx xx xx 25     System Net Sockets Socket DoConnect EndPoint endPointSnapshot  SocketAddress socketAddress   208    System Net ServicePoint ConnectSocketInternal Boolean connectFailure  Socket s4  Socket s6  Socket amp  socket  IPAddress amp  address  ConnectSocketState state  IAsyncResult asyncResult  Exception amp  exception   464   WebException  Unable to connect to the remote server     System Net ServicePoint GetConnection PooledStream PooledStream  Object owner  Boolean async  IPAddress amp  address  Socket amp  abortSocket  Socket amp  abortSocket6   6486360    System Net PooledStream Activate Object owningObject  Boolean async  GeneralAsyncDelegate asyncCallback   307    System Net PooledStream Activate Object owningObject  GeneralAsyncDelegate asyncCallback   19    System Net ConnectionPool GetConnection Object owningObject  GeneralAsyncDelegate asyncCallback  Int32 creationTimeout   324    System Net Mail SmtpConnection GetConnection ServicePoint servicePoint   141    System Net Mail SmtpTransport GetConnection ServicePoint servicePoint   170    System Net Mail SmtpClient GetConnection    44    System Net Mail SmtpClient Send MailMessage message   1554   SmtpException  Failure sending mail      System Net Mail SmtpClient Send MailMessage message   1906    Admin Alert SMTPAuth   in c  Users spandya Documents Visual Studio 2012 WebSites WebSite3 Admin Alert aspx cs 61    Admin Alert Page Load Object sender  EventArgs e  in c  Users spandya Documents Visual Studio 2012 WebSites WebSite3 Admin Alert aspx cs 22    System Web Util CalliEventHandlerDelegateProxy Callback Object sender  EventArgs e   51    System Web UI Control OnLoad EventArgs e   92    System Web UI Control LoadRecursive    54    System Web UI Page ProcessRequestMain Boolean includeStagesBeforeAsyncPoint  Boolean includeStagesAfterAsyncPoint   772   What else I am missing here  Firewall inbound rules are there for these specific port addresses

User · Answer

Windows Firewall was creating this error for me  SMTP was trying to post to GMAIL at port 587  Adding port 587 to the Outbound rule  Outbound HTTP SMTP RDP  resolved the issue

User · Answer

Ok  so very important to realize the implications here    Docs say that SSL over 465 is NOT supported in SmtpClient    Seems like you have no choice but to use STARTTLS which may not be supported by your mail host  You may have to use a different library if your host requires use of SSL over 465   Quoted from http   msdn microsoft com en-us library system net mail smtpclient enablessl v vs 110  aspx  The SmtpClient class only supports the SMTP Service Extension for Secure SMTP over Transport Layer Security as defined in RFC 3207  In this mode  the SMTP session begins on an unencrypted channel  then a STARTTLS command is issued by the client to the server to switch to secure communication using SSL  See RFC 3207 published by the Internet Engineering Task Force  IETF  for more information   An alternate connection method is where an SSL session is established up front before any protocol commands are sent  This connection method is sometimes called SMTP SSL  SMTP over SSL  or SMTPS and by default uses port 465  This alternate connection method using SSL is not currently supported

User · Answer

If the other answers don t work you can check if something else is using the port with netstat   netstat -ano   findstr  lt your port number gt   If nothing is already using it  the port might be excluded  try this command to see if the range is blocked by something else   netsh interface ipv4 show excludedportrange protocol tcp

User · Answer

Please confirm that your firewall is allowing outbound traffic and that you are not being blocked by antivirus software     I received the same issue and the culprit was antivirus software

User · Answer

Do this if you are using GoDaddy  I m using Lets Encrypt SSL if you want you can get it    Here is the code - The code is in asp net core 2 0 but should work in above versions   using System  using System Collections Generic  using System Linq  using System Threading Tasks  using MailKit Net Smtp  using MimeKit   namespace UnityAssets Website Services       public class EmailSender   IEmailSender               public async Task SendEmailAsync string toEmailAddress  string subject  string htmlMessage                        var email   new MimeMessage                email From Add new MailboxAddress  Application Name    applicationId gmail com                 email To Add new MailboxAddress toEmailAddress  toEmailAddress                email Subject   subject               var body   new BodyBuilder                               HtmlBody   htmlMessage                             email Body   body ToMessageBody                 using  var client   new SmtpClient                                    provider specific settings                 await client ConnectAsync  smtp gmail com   465  true  ConfigureAwait false                   await client AuthenticateAsync  youremailid gmail com    sketchunity   ConfigureAwait false                    await client SendAsync email  ConfigureAwait false                   await client DisconnectAsync true  ConfigureAwait false

User · Answer

I got this error   System Net Sockets SocketException  An attempt was made to access a socket in a way forbidden by its access permissions   when the port was used by another program

User · Answer

I had a same issue  It was working fine on the local machine but it had issues on the server  I have changed the SMTP setting  It works fine for me   If you re using GoDaddy Plesk Hosting  use the following SMTP details   Host   relay-hosting secureserver net Port   25

[c#] "An attempt was made to access a socket in a way forbidden by its access permissions" while using SMTP

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