When I took VR in 2013 I was called into office and shown VR figure on pc by manager and given a printout and told I could decide if I wanted to accept or think about it and come back the next day. I wasn't sure what he meant about working my notice or working half of it or leaving without notice, so I said I'd get back to him. I had a word with the Area Rep who said PILON wasn't paid any more, so I went back the same day and told the manager I wanted to accept the offer and work my 12 weeks notice.
It took another four weeks to get the formal VR offer letter, which had to be signed and returned within 14 days.
If you have only been shown an email it would be just to know if you are interested in accepting the offer.
You have to be sent the formal offer in writing which you have to sign and return before it is binding on you, and RM aren't committed to giving it to you until they send you the letter with your Last Day of Service.