Try switching to POP, I have used that historically with Outlook Express and Thunderbird and apart from a relatively short period at the beginning of the problem that has worked normally.
If you use IMAP that will continually be trying to sync the folders, and it is the server folders they are having problems with so that will be reflected into whatever client you use.
Webmail came and went over the first few days but because I use a PC client and store messages locally with POP I've never used Webmail folders and their loss has had no effect on me. Apart from briefly the primary Webmail account worked, one of the secondaries also did but the other didn't for several days with an error message. That came back, then several days ago both went with just an exclamation mark in a triangle and haven't been back since. but as I say they are both working with POP in Thunderbird.
I really can imagine Virgin giving up on this altogether. After discovering a while back they no longer issue new email accounts I felt it was the thin end of the wedge and created a Gmail account so over the last few days have been changing everything over to that. Not a trivial task - getting-on for 100 organisations of all types mostly done now, plus a lot of personal contacts barely started yet.
Never, ever, keep important stuff in 'the cloud'.
But out of the hundreds of posts in this and other threads I wonder how many people ask a question then bother to read subsequent posts for a useful response.