After receiving 100's of 'email undelivered' messages in all my email inboxes I opened, not the emails, but the properties sheet to view the source code and as other people have found out, these were supposed to come from me, the return path was empty, and copies were sent to other emails (real or faked).
Around the same time some emails I did send disappeared into the ether. My computer started slowing up etc... so I suspected a virus. AVG didn't detect anything neither did Malwarebytes. After some struggle to install another antivirus prog I was successful with Avira which I ran and lo there were 3 instances of a trojan found. Multiple installs/recoveries later the OS became stable and further virus checks with Panda, Malwarebytes, MS online checker and Eset online didn't find any more virus. (after removing the virus's, Avira kept crashing the HD making it non-bootable so was removed).
Before the system had become unstable I had created rules in Outlook Express (yes I'm still using this, in Win XP) which stopped the spam mail from being downloaded while deleting from the server.
Since the recovery process has removed the rules, I still find some in 1 account.
A search on mxtools.com shows that my accounts have been blacklisted on 4 from 95 lists. This I thought might explain why some emails I'd sent had gone astray.
So:-
1. Do I have to change my email addresses to stop these spam mailings and/or blacklisting?
2. Can't PN filter out such messages?
