I’m able to get smtp message sent to a 3rd party smtp server when I test locally but not when I port this code to our dev server. When I try it there, I can’t really tell but I think it’s not sending out a request. I ran firebug, fiddler and did not see a request from my code that’s sending the mail request.
Other than testing the hosts’s smtp endpoint that I’m sending this smtp request to to ensure it’s open to us (which it is), I am stuck trying to figure out why the same code works on my machine but not our Windows Server 2008 R2 dev box.
Are you sending out the mail directly to the 3rd party smtp server from code or routing through a local SMTP server on the 2008 box?
If you’re not routing through (say) an SMTP service in IIS on the 2008 box, you could try this, configuring your app to use the local service, and set the following in code to drop mail into a folder structure under IIS allowing the SMTP service to take care of the delivery of the email
smtpclient.deliverymethod = smtpdeliverymethod.pickupdirectoryfromiis
you could then configure the logging for the local smtp server and check to see the conversation between the local and remote servers to identify the problem. You’ll also be able to see the folders used for queuing mail and the actual email envelopes within there (if you’re quick)
have you checked a connection to the remote smtp server from the 2008 box using telnet to open up a conversation with it to negate any firewall issues?
If emails are still failing to go through to the third party SMTP server maybe its a deliverability issue that’s causing your problem. Is your servers IP address allowed to send email for the domain it is, if not you might need to post an SPF record against the domain for the IP address of your DEV box.