Honing in Win98?

I have configured Outlook with 2 pop accounts.
One via LAN to our business Exchange server, the other via ISDN to an ISP and a private account.
Since the ISP does not allow sending mail from another network, I had to configure the other account tocall the ISP to send mail.

The problem is:
The second account will not send mail through the ISP.
Could the problem be that the ISDN connection is to swift for the IP-address to be changed to an acceptable one for the ISP?
An, if so, whats theremedy?

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Tron