does this mean that virgin media emails not secure?
No it does not mean that VM emails are insecure.
The main body of the email is sent securely but most images in emails are linked to external web servers.
If the images in the email you are viewing use HTTPS your browser will not trigger a warning but if the images use HTTP links (and in my experience most do) then this triggers the 'Not Secure' warning. Confusingly, in many browsers that warning remains after you have stopped viewing the email that triggered it until you reload the whole page.
You can test whether this is the issue by checking and if necessary changing a setting in VM Webmail:
Click on the horizontal bars (1), then "Settings" (2), then "Email" (3) and ensure that the "Allow preloaded images" is unticked.
Go back to "Email" and reload the page. When you view an email with links to an image you will see the browser shows no warning but when you click on the "Show images" box the image will display and you will get the warning in your browser.
Although no-one else can see the email itself, the browser displays the warning because it is possible for a third party to see the images that are being sent and possibly modify them.
It is good practice to leave the box in (4) unticked so external images are not automatically displayed and to manually allow mages to be downloaded only with emails from senders that you trust.
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