Problem sending email with all email clients

[DWalrus]

I have a small home network running with a SpeedStream DSL modem, connected to a router. From the router I have six computers connected.
I use Netscape (Mozilla) as my email client. My wife uses MS Outlook. We are running XP Pro. For three days now we are having problems sending email. We can receive and can surf the internet just fine. I can send and receive email with my Yahoo account.
My ISP provider says it's the router. The router tech support says it's the ISP. When we attempt to send email, 99% of the time it fails, times out, whatever you want to call it. The error says to check the SMTP settings.
All the settings have been checked and are okay. The settings on the router check okay. I can disconnect the router and connect just my PC and the email works fine.
The only thing that has changed is that I replaced the motherboard in my PC this past week. The hard drive and all the setup otherwise is the same.
I do have Zone Alarm Pro and McAfee VirusScan running. I have disable one, then the other, then both without having any change in the email problem.
I think it is in the router. Let me hear everyone's take on this one!

Thanks,

DWalrus

 

[DWalrus]

For the record...

After many days of trying everything possible, I bought a new router and THAT was the problem. It seemed obvious but the manufacturer swore it was the ISP.
Oh the little things we take for granted!

DWalrus