CDOSYS Woes

I'm putting all my points on this one in the hopes that i can finally get some questions answered about my CDOSYS problems.  I've been writing applications for my employer that send emails programmatically, and I've been using CDOSYS.  While experimenting with the package I discovered a major problem : that there seemed to be a difference between the emails sent to people within the company (our mail is provided by an MS exchange 5.5 server) and those sent to addresses outside of the company (I am guessing because they are outside of our firewall, but i don't know.)

After endless experimentation and frustration i discovered that a CDO.Message that referenced our main server (NT server 4 with MS exchange 5.5) as it's mail server would deliver messages internally to the company.  Another machine on the network, running IIS and win2k, would deliver external messages when referenced.  (to be thorough: the NTS machine cannot deliver external mail, and the win2k machine cannot deliver internal mail.)

Given a long list of emails, it's a pretty big pain in the butt for every program that i write to have to sort them into local and external addresses, then send the messages to two different servers.

Not only this : as of three days ago, the computer that I use to send external messages stopped working.  The emails began bouncing back with the error message "Unable to deliver message to the following recipients, due to being unable to connect successfully to the destination mail server."

I would like to get to the bottom of all this trouble and just use one mail server to send emails programmatically, something that is supposed to be easy with CDOSYS.  Below is a sample of the code I use to send messages.  The successful answer will receive 385 points + my eternal gratitude.

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Set extMailConfig = New CDO.Configuration
Set Flds = extMailConfig.Fields
With Flds
  .Item(cdoSendUsingMethod) = cdoSendUsingPort
  .Item(cdoSMTPServer) = (win2k/IIS Machine)
  .Item(cdoSMTPConnectionTimeout) = 30
  .Item(cdoSMTPServerPort) = 25
  .Item(cdoSMTPAuthenticate) = cdoAnonymous
  .Update
End With

Set intMailConfig = New CDO.Configuration
Set Flds = intMailConfig.Fields
With Flds
  .Item(cdoSendUsingMethod) = cdoSendUsingPort
  .Item(cdoSMTPServer) = (NTS4.0/Exchange Machine)
  .Item(cdoSMTPConnectionTimeout) = 30
  .Item(cdoSMTPServerPort) = 25
  .Item(cdoSMTPAuthenticate) = cdoAnonymous
  .Update
End With

' Send an external message.

Set extMail = New CDO.Message
With extMail
  Set .Configuration = extMailConfig
      .bcc = bcc
      .To = externaladdress@externalserver.com
      .From = mailfrom
      .Subject = "test"
      .TextBody = "This is a test."
      .Send
End With

' send a local message.

Set intMail = New CDO.Message
With intMail
  Set .Configuration = intMailConfig
      .bcc = bcc
      .To = localaddress@myserver.com
      .From = mailfrom
      .Subject = "test"
      .TextBody = "This is a test."
      .Send
End With

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