SharePoint custom email not shooting, How to fix this?

Question

Hi All,
I trying to send custom email from C# to external user, but mail is not going. But sending to same domain users and find these exceptions in log;
"Type: SmtpFailedRecipientException, Exception Message: Mailbox unavailable. The server response was: 5.7.1 Unable to relay"
"Exception thrown from business logic event listener: System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: 5.7.1 Unable to relay     at System.Net.Mail.SmtpClient.Send(MailMessage message)    
at ChangeControl3_Nov.eGA_Utility.SendmailnoAttach(String To1, String subject1, String Body1, String frommail1, String FS) in c:\Users\acpbsdt\AppData\Local\Temp\2\Vsta\6c9090f9672f4fba89c20855a223734b\eGA_Utility.cs:line 288     at ChangeControl3_Nov.FormCode.SendBothCTRL256_5_Clicked(Object
sender, ClickedEventArgs e) in c:\Users\acpbsdt\AppData\Local\Temp\2\Vsta\6c9090f9672f4fba89c20855a223734b\FormCode.cs:line 417     at Microsoft.Office.InfoPath.Server.Util.DocumentReliability.InvokeBusinessLogic(Thunk thunk)     at Microsoft.Office.InfoPath.Server.SolutionL...
08e3e29c-259c-60b9-fdb2-5829cbd6a566"
Any idea? Thanks in advance!

Answer 1

Hi,
Please check the links below:
The server response was: 5.7.1 Unable to relay -- Help Please
http://forums.iis.net/t/1165876.aspx?The+server+response+was+5+7+1+Unable+to+relay+Help+Please
Mailbox unavailable. The server response was: 5.7.1 ... we do not relay
http://www.codeproject.com/Questions/94257/Mailbox-unavailable-The-server-response-was
If you want to customize code for send Mail in SharePoint using C# .net code, here is a blog for your reference:
https://technologykhabar.wordpress.com/2013/06/19/custom-code-for-send-mail-in-sharepoint-using-c-net-code/
The code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Mail;
using Microsoft.SharePoint.Administration;
namespace SendEmail
class Program
static void Main(string[] args)
SPWebApplication webApp = SPWebApplication.Lookup(new Uri("https://serverName/"));
MailMessage mail = new MailMessage();
mail.From = new MailAddress("[email protected]");
mail.To.Add("[email protected]");
mail.Subject = "Subject Test";
mail.Body = "Body Test";
// SmtpClient class sends the email by using the specified SMTP server
SmtpClient smtp = new SmtpClient(webApp.OutboundMailServiceInstance.Server.Address);
smtp.UseDefaultCredentials = true;
smtp.Send(mail);
Best Regards
Dennis Guo
TechNet Community Support