I had/have the same problem. Did the malwarebyte scan on all 4 pcs and although no malware came up one pc had lots of stuff it suggested should quaratined. Appearing on Spamhaus and requesting a delisting has become a daily chore.
In brief, I switched to a friend's ISP (not Virgin) to check this out. Used whatsmyip, entered into Spamhaus and a PBL error was flagged up. According to the information given there is a smtp authentication problem. I definitely have the correct SMTP settings. I cleaned again and delisted. Next day, again the PBL error popped up. Perhaps this has something to do with the not-Virgin ISP I am using? I have not checked this before when using the not-Virgin ISP, although it looks like the emails are working normally in Outlook 365. It will be a couple of weeks until I can get back to my Virgin network.
There is nothing wrong with being on a PBL - or Policy Block Lists
These lists don't identify spammers, rather they identify IP addresses that should not be hosting MAIL SERVERS A perfect example is residential IP addresses which are allocated by DHCP. These connections IP addresses MAY change without warning, which is not something you want on a mail server.
Have a read at my post here to see where blacklists normally kick in.
I've read the bit on Spamhaus that talks about SMTP authentication, and to be frank, if I worked for Spamhhaus I wouldn't have posted that.
Normally XBL and SBL issues wouldn't affect email clients either, but Virgin Media have chosen to to reject logins where the users IP is on the CSS list.
To be frank, I don't blame them. If you are on the CSS it means that your IP has been seen spamming in the last 48 hours. If you're not knowingly spamming (and most aren't) it means that something on your network has been infected with malware and is attempting delivery to mail exchangers. The fact that you've delisted yourselves and then been re-listed would confirm this.
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