The real reason why my SMTP couldn't send

Avast Free Antivirus / Premium Security
1

I am using Avast 4.6 and Win XP Home. I had the same problem when I was using Win98se(no firewall then)

My ISP SMTP sends well, but the other SMTP can’t send. So I ISP’s smtp to send email and it worked well.

I heard about ISP blocking port 25 from SMTP other than theirs.

Today I called SBC (used to be Pacific Bell) and found it really is them that blocked the port 25. I asked them to unblock it and reboot the pc and DSL modem. Now my long-idled other smtp server are sending well, actually both ISP email’s SMtp and the other pop email’s SMTP are sending fine.

Problem solved.
I guess someone else may have the similar problem and blaming Avast and trying do with firewall.

2

Nice that they didn’t mention blocking port 25, sometimes they do this but allow port 26 for SMTP.

Thanks for mentioning it, I’m sure it may well help others.

Welcome to the forums.