Lonny, you have a conflict in port 25 (SMTP or OUTGOING MAIL), I mean, two programs are trying to use the same port to connect the Internet. To help you, I need to know what is happening. Can you download
TCPView, run it and see what programs are connecting the port 25?
If you want to 'work in the dark', I mean, without knowing and just following orders (plain language as you asked) so:
1. Open your C:\Program files\Alwil Software\Avast4\Data\avast4.ini file
2. Search for [MailScanner]
3. See if you have a line with this
SmtpListen=127.0.0.1:26 If not, write it exactly this. I will scan at port 26 and not at 25.
Hope this help