Hi Jae,
Thanks for your comment.
I have run every check I can think of, including rootkit checks on server and nothing is showing.
I have also shut my server down for 48 hrs (shutdown and powered off in hosting control panel), and during this I got blacklisted again.
I also have got dmarc report; which states that over 3100 emails were detected as possibly coming from my domain; but only 30 had fully passed the dmarc and spf checks as valid emails ( which after checking were the 30 I had sent).
Thats means that over 99% of emails dmarc had notices were not from my domain.
This is really anoyhing, and takes a lot of daily checking and delisting.
ANy other ideas?