.NET SMTP Client - Client does not have permissions to send as this sender

Question

I\'m getting strange occurance on our servers when I am trying to send an email using SmtpClient class via an ASP MVC3 project. This is the code I am using.

Answer 1

It is likely that the mail server does not support sending anonymous emails and will require credentials to be specified which are registered on the mail server.

You can specify the credentials like so:

client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential("username", "password");

Hope this helps.

Answer 2

For me it was using different credentials -

In network credentials I was using -

new NetworkCredential(smtpUser, smtpPassword)

and in fromAddress

 var fromAddress = new MailAddress("anotheruser@gmail.com", string.Empty);

Where when sending email where fromAddress is different than actual network credentials will lead this issue. See below -

 using (var message = new System.Net.Mail.MailMessage(fromAddress, toAddress)
                {
                    Subject = Keys.MailSubject,
                    Body = body,
                    IsBodyHtml = true
                })
                {
                    smtp.Send(message);

                }

The simple fix is to keep both the mails same as network credentials's one.