SMTP question re: outgoing email (got trubbles, folks!)

ISP is Mindspring/Earthlink; Email is Eudora.

Lorda mercy me...for several months I was getting emails from my ISP about how I needed to update my settings so that I could continue to receive emails through their server. Finally, after so many reminders I did what the suggested. All it was was changing my SMTP address.

Once I did that I discovered I could still receive emails but could no longer send them! bummer.

I was on "online chat help" for over an hour once nite with them. We did this, did that; some where along the line I turned off my firewall and anti-virus, did this and that again. Sent an email and it worked. However!...

Later on, when I noticed the firewall/anti-virus still turned off, I turned them back on, tried to send a message and again, no go!

ISP (via email) says basically "do what we told you to do in the beginning"...which of course doesn't help.

In the meanwhile, I've discovered it is not my firewall (zonealarm) that is stopping outgoing emails. I can turn off my anti-virus (Avast) and send emails just fine. And now, of course, ISP say to contact them.

What gets me is all was working perfectly well before I make the SMTP change; now they say I have an "avast" problem. (I really wish I had written down my original setting before I changed the SMTP.)

Is there anything ya'll can think of that I can check? I've reset my email "personalities" and made sure they were correctly set up. I've double-checked my avast settings, allowing SMTP, etc.

Anyone else having to go thru this?