Question : Software can't send mail through SMTP any longer with new configuration.

A new client switched ISP's over from Bellsouth to a T1 provider here in Atlanta and during the transfer the smtp connector was changed from mail.bellsouth.net with authentication to a new connector that routes all outgoing mail using DNS.  Exchange is able to send and receive mail now without a problem, but there was a custom developed software package on the domain controller that occasionally sends out mail to clients on a mailing list.  

The software package was before using smtp.bellsouth.net on port 25 and now it's unable to send out.  I've used the SMTP servers that the new ISP has, but they won't send out without authentication.  

Is there a way that this software package can route mail through the exchange server?  

I've already tried using the private IP address of 192.168.1.15 with port 25 in the software package, as well as 127.0.0.1.  I know absolutely nothing about this software package other than they can change the outgoing mail server and that's all.  

Any ideas?

Answer : Software can't send mail through SMTP any longer with new configuration.

Hmm... good question.  :)

It should depend on the name you specified in the custom software package - if you used 'localhost' then I'd use 127.0.0.1 otherwise use the IP that name you specified resolves to.

So if the command:  nslookup server.domain.local
resolves to: 192.168.0.100
add the IP address: 192.168.0.100