The thing is it shouldn't have been a dead post IMHO. Howard was merely pointing you to a post suggesting what was going on, and in fact, I'd missed that there had been no Forum Team interaction in that post until you posted in it.. So he may have actually done you and anyone else having the same problem a favour.
At least now the Forum Team have jumped into that thread and raised the issue, BUT this is as much down to o2 as it is to Virgin Media.
There are certain standards that mail transport is expected to adhere to and o2 aren't following them. So they look to all the world to be a spammer, but rather than filter mail as potential spam connections from the server are being rejected. This has been a de-facto standard way of fighting spam for decades, yet surprisingly some of the big companies still get this wrong. Coenoby did a lot of good in that thread..
Received: from ukmlwmsw004.uk.pri.o2.com ([158.230.100.102])
by mx.google.com with ESMTPS id h3si13063831wru.429.2021.03.28.01.44.13
Tells me a lot as I really have put my head down the rabbit hole when it comes to understanding email. (I have my own server which does follow best practices in terms of rDNS SPF DKIM and DMARC
I personally think you owe Howard an apology, he really was trying to help.
Incidentally, you've now marked your post as solved by clicking the Helpful answer button, you might want to unmark it.
Tim
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