Did you use the Mail Protection Wizard after avast! installation?
Which application is using the port 25? (use
TCPView to enumerate all active TCP and UDP endpoints, resolving all IP addresses to their domain name versions. TCPView shows the port numbers and the name of the process that owns each endpoint.
Do you use any spam killer application?
Which is your OS? What email program are you using?
As you can see, to help you we need more information...
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