How do I send emails outside my domain with Exchange 2007 and c#

Question

I am able to send emails using the typical C# SMTP code across Exchange 2007 as long as both the from and to addresses are within my domain.

As soon as I try to send emails outside the domain I get:

Exception Details: System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: 5.7.1 Unable to relay

How can I get exchange to accept my email and send it out to the internet?

Solution 1

Try #2... How about using a Exchange Pickup Folder instead? They are a faster way to send emails through Exchange because it just creates the email and drops it in the folder, no waiting to connect to the server or waiting for a reply. Plus I think it skips the whole relay issue.

Configure youur SmtpClient like so:

SmtpClient srv = new SmtpClient("exchsrv2007", 25) {
    DeliveryMethod = SmtpDeliveryMethod.SpecifiedPickupDirectory,
    PickupDirectoryLocation = "\\exchsrv2007\PickupFolder"
}
...

Solution 2

Authenticate to the exchange server.

http://msdn.microsoft.com/en-us/library/system.net.mail.smtpclient.credentials.aspx

---

DefaultNetworkCredentials returns empty strings for username etc and causes this exception...

Here is an example, and here is another of sending authenticated message with System.Net.Mail.

Solution 3

You'll need to get your exchange admin to configure exchange to allow sending outside the domain. In my experience they've been reluctant to do so because of spam concerns.

If its' for limited use, you can set up server-side rules in exchange to forward messages meeting certain criteria outside the domain. You might be able to use VBA in these as well to pretty things up, but I am not sure.

Comments

[jmcd]

I've followed this artice and it didn't make any difference :(

[jmcd]

DefaultNetworkCredentials returns empty strings for username etc and causes this exception: Mailbox unavailable. The server response was: 5.7.1 Client does not have permissions to send as this sender

[scottm]

+1 Usually larger corporations have multiple exchange servers and at least one is allowed to forward email outside the domain.

[nuthan ratnam vara]

Not by default, the network path would need to be shared and the process ASP.NET is running as (or the impersonation) would need permissions to access the directory.

[Xavier Young]

Can you tell most of my experience with Exchange has been with smaller companies :D

[Mozy]

+1 for such a time saving solution. Solves my problem perfectly.

[Chris Snowden]

+1 client.Credentials = CredentialCache.DefaultNetworkCredentials; solved my relaying issue. Relays fine using this.