There really is only one way to stop these problems with Virginmedia emails, and that is to move to a different email provider. VM stopped issuing new email addresses two years ago, and the lack of support since then shows that they really can't be bothered to maintain the existing accounts.
There has been frequent speculation about whether VM is going to close their email service altogether, and although no official statement has been made, some users have reported on here that they have been told on the phone that it will be closed.
Moving to a separate email service also means you are not locked into one broadband provider if you need to change for any reason.
The easiest way to start the move to another email account is to set up an auto forward on your VM account so that all incoming mails are sent to the new account, and to reply to them from the new account. You will then be well on the way to being freed from all the difficulties you have been experiencing.