I am using sendmail in my DMZ and exchange 2007 for my internal mail server. This was configured before I started here and is not likely to change soon. The problem I inherited is this When a client goes to our web page and puts in contact info. 2 emails are sent. 1 internally to our sales dept. and 1 to the client with an attachment. The internal email is recieved fine. The external email always fails nomatter who it is, with error (#5.1.2 SMTP; 550 Host unknown> #SMTP#)
It says the generating server is the sendmail server in the DMZ, not the exchange server, on the NDR report i recieve. The exchange logs do not show any errors for these emails. As a matter of fact i cannot find them at all.
The autoreply process:
When a visitor to our website submits a form, the application attempts to send 2 messages. One to us, which is the content that the web visitor submits, and the other as an "auto-responder" which thanks the visitor for their request. The first email gets delivered fine
The application that is attempting to send the email is a Perl Form processor. It sends to the default location of the SMTP server configured on the web server. This in turn is forwarded to the exchange server via an alias that's configured on the web server. this alias is internalmail.server.com, which the web server is assuming has SMTP service available.
Please help me solve this issue,
Thanks

You get this figured out yet?

If not, some questions for you:
Sounds like the sendmail is set up to use itself as the Mail server. Is the firewall blocking port 25 from the DMZ to external?

If the sendmail is using the Exchange 2007, Is this program authenticating into the SMTP server, or is the IP address allowed to relay?
Sounds like it may have right to relay internally, but not externally.
It may be the sending email address, I have seen some servers block relay if the email address does not match the account it authenticates with (Especially with Exchange 2007)

I would run Wireshark on the server in the DMZ and the SMTP server while sending a test to see what the error is.

1 members found this post helpful.