anim,
Ok...the guys have offered excellent guidance but I think we need to go back to basics here.
Your version apparently has a corruption somewhere in the On Access Protection module.
Therefore I suggest that we start "anew" and have you uninstall Avast4.0, download a new version which should be 4.1.268.
In 268, you will have 5 On Access Protection modules and each will allow you to configure it to work best with your application be it MS Outlook/Exchange or OE.
The new installation should set your server address to 127.0.0.1 as before. Port 25 is used by the default email client for SMTP service, and Port 125 is for the Pop 3. My OE6 uses these and I have never had a problem with Avast.
As I said before, make MSOE your default mail handler, check the port and server settings and try it again after updating to build 468.
I think we have too much going on between MSOE and OE6 that Avast may only "see" one of them without real careful configuration.
Do you use a firewall or proxy server at all?
We'll get it running for you....
but please lets be on the "same page" here. Get 4.1.268 so that we both are using the same version of Avast and mail clients. It makes things easier for me to analyze and explain to you.
Ok....Good luck.

PS: Sorry for the log post, but I tend to think things out as I type. I usually tire out about 2am. hahaha