The server response was: 4.3.2 Service not available, closing transmission channel

Question

I am getting this error while sending email from my application. Can anyone suggest any solution.

Service not available, closing transmission channel. The server response was: 4.3.2 Service not available, closing transmission channel

Below is code.

string adminID = "AAA@tu.edu";
MailMessage msg = new MailMessage();
msg.From = new MailAddress(adminID);
msg.To.Add("BBB@ttu.edu");
msg.Subject = "Sample Email";
msg.Body = "Hello ";
SmtpClient SmtpMail = new SmtpClient();
SmtpMail.Host = "basic.smtp.ttu.edu";
SmtpMail.Port = 25;
SmtpMail.Send(msg);

score 21 · Answer 1 · answered Oct 12 '12 at 16:06

21

Got the solution for the issue. The Server was rejecting the request because this application didn't have write rights on that server. The code was perfectly fine, just it was permissions problem. Hope this helps someone!

answered Oct 12 '12 at 16:06

techblog

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1. I've never had any permissions issues using system.net.mail. 2. How would one get rights while testing on a dev box? – user609926 Apr 18 '17 at 15:18
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You might need to add your IP address to the firewall for the exchange server. – Gandalf458 May 11 '17 at 19:38

score 2 · Answer 2 · edited Dec 27 '21 at 19:42

2

Please check whether the server which is sending the e-mail is whitelisted on the SMTP server or Exchange server.

I had the same issue and whitelisting it on SMTP server resolved my issue.

edited Dec 27 '21 at 19:42

answered Jan 06 '21 at 15:23

Suprotim Roy

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The server response was: 4.3.2 Service not available, closing transmission channel

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