[fChk]

Thank you for your detailed explanation @fChk.  This may or may not have anything to do with this, but a few months ago I'm almost certain I was a victim of DNS hacking.  I was wondering whether this could be related to your topic along the lines of "leaking a site's identity".

Not exactly related.. This thread is about the end-users privacy issues.

First of all, sorry about that misfortune.

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I then asked Contabo for a new IP, and up to a couple of months ago, about three months after the event, those domains seem to be still "abandoned" with my original "hacked" IP still in place.  Do you think someone else could become a victim if they were to get a VPS with the IP with which the two domains are registered with Namecheap?  In essense DNS hacking?  Like Namecheap and other domain regisrars who do not verify IP ownership when domain DNS is made custom to an external IP actually open up the possibility of domain DNS abuse?

Anyone can become a victim when they have a static IP. I don't think it's a DNS poisoning issue here, as if I understand what you're saying above, the issue was the IP not the domain name. Thus, in this case, it should have been an IP address spoofing incident; but that's quite unlikely IMHO. (for more on this.)

I was also thinking of another possibility.  While those rogue Websites may have been hosted somewhere with my "attack" IP before I was given the IP, could they have set up e-mails in such a way that their sending were delayed and then launched after they no longer were hosted with that IP?

This is a more likely scenario than the IP address spoofing (what are the odds?!!)