SMTP email using c#

Posted on 2006-07-17
Last Modified: 2012-06-21
Hello experts,

I am trying to send emails via a web application. when i test it on my local machine, it works fine. But when I upload to the live server it doesn't. I am using the follwoing line to send;-

Utils.Mail.MailSender.SendMailMessage("Localhost", msgWithAttachment);

I got the following code off the internet somewhere;-

Response.Write(bthcu.Message + bthcu.StackTrace);

This outputs the following when the email is not sent;-
Mailbox unavailable. The server response was: 5.7.1 Unable to relay for at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at Utils.Mail.MailSender.SendMailMessage(String SMTPServer, MailMessage message) in C:\VS2005Projects\EasyMailSender\EasyMailSender\MailSender.cs:line 83 at valuation.ImageButton1_Click1(Object sender, ImageClickEventArgs e) in c:\Inetpub\wwwroot\livesite\valuations\valuation2.aspx.cs:line 212
Question by:claracruz
LVL 23

Expert Comment

ID: 17120954
Hi claracruz,

You might need to use the server's name.  Also check if you need to authenticate against the mail server as i think this is whats happening, if so you need to add smtp fields

LVL 23

Expert Comment

ID: 17120958

this code demonstrated how to incorporate username and password

Expert Comment

ID: 17121027
Hi claracruz

Here is code which I generally use in my applications

System.Web.Mail.MailMessage mm=new System.Web.Mail.MailMessage();
                  mm.Body="Hi, test";                  

System.Web.Mail.SmtpMail.SmtpServer="Name of the SMTP server name which your live server uses";


Harshit Sheth
LVL 23

Expert Comment

ID: 17121063
this error:

The server response was: 5.7.1 Unable to relay for

generally means that the server cannot reack the domain - probably because you need to authenticate yourself as a sender - i dont think it is the code that is the problem
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Expert Comment

ID: 17121353

Expert Comment

ID: 17121778

Author Comment

ID: 17129436
kaliyugkaarjun ,
My code works on my local computer, I know the code is not the probelmAnd am using c#.

apresto ,
How do i  authenticate myself as a sender - i know its not a code problem as it works on my local machine. What I need to know is how to configure my webserver/smtp server to send emails

Many Thanks,


Accepted Solution

harshits earned 500 total points
ID: 17136118
This seems to be the solution to your problem. Just check this...

" A little googling to learn what the 5.7.1 error is, from which I deduce that the Exchange server is refusing to relay for anyone not in its domain. So I look again at the From and To addresses. Ok, well, one problem is that I misspelled the From address. A few more experiments, and I learn that our internal relay server will send only from and to addresses within our domain. (Or so it seems.)

Anyway, now it works.".....

Harshit Sheth

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