Thanks for confirming. Are you trying to load your Virgin emails through Apple Mail? Or are you just experiencing slowness when loading up the app?
Are you also having issues with any other devices or suffering from slow speeds when browsing the internet?
I'd start by putting your Mac in Safe Mode (this may help speed things up). You can boot up Safe Mode by holding down the Shift key while your Mac is starting up. Once the log in window appears, you can then release the Shift key and log in as normal. Try loading up your mail again from there and let me know if you see any difference.
I use the Apple Mail. The app opens just fine and any emails download OK, also any emails I send go quickly. It is only when I click the get mail icon that it take nearly a minute to get any mail or tell me there are no new messages. It is not all the time but does happen frequently and I have only been experiencing the problem within the last 6 weeks or so. If it were consistent then putting my Mac in safe mode might be of value but there are no indications this would be of any value. I am not experiencing any other problems with other devices or slow speed when browsing the internet.
My mail app is knocking on Virgin Medias' email and Virgin Media is taking a long time to answer the door.
Since it is not consistent, removing my and my wife's Virgin Media email address and readding it isn't going to do anything. I don't think I have ever signed into Virgin Media's web, I have always used the Mac mail. Like I said, it has been fine until recently.