If they do not issue you with a barcode that can be shown on any device (or printed) then it's not an e-ticket.
If it can only be shown in an app and has to be activated then it's an m-ticket.
On Friday I travelled from Sheffield to London King's Cross via Doncaster, using the 14.51 Bradford-King's Cross Grand Central train from Doncaster. I used a so-called e-ticket (which is actually an m-ticket) downloaded to the GC app, but I couldn't for the life of me work out how to activate the ticket on the day of travel. The GC website at
www.grandcentralrail.com/tickets/ticket-types/e-tickets/ shows you how to activate your ticket, but the app on my phone didn't appear to have an "activate", "enable" or "release" button even when I tried to access it on the day of travel.
I am guessing that this could be because my phone has an older version of Android than 6.0. I've recently got a new phone, but I think it's a now discontinued model that was already being phased out when I got it. The GC website says you need to have iOS version 9.0+ or Android version 6.0+, so maybe if you have an older version you can still download the app but not all of its capabilities, including m-tickets, will work properly.
So I simply showed the e-ticket notification on the app to the guard on my Northern train from Sheffield to Doncaster, who luckily accepted it without question even though it was an earlier train than the CrossCountry train on which I was booked (which would only have given me about a 10-minute connection at Doncaster).
There was no ticket check on the Grand Central train, but the ticket gates at King's Cross were in use. Had I been able to download my m-ticket, I might have been able to open the gates by swiping the barcode on the reader, but as it was I had to ask to be let through manually. If there had been a ticket check on the train, I could potentially have been treated as not having a valid ticket.
In future I had probably better stick to print-at-home or traditional paper tickets when travelling with GC, unless any other operators' websites, such as LNER or East Midlands Railway, that offer proper e-tickets will sell me one for GC.
In fact, it would appear that you can book e-tickets for GC using the LNER site. See also the thread on e-tickets on LNER at
https://www.railforums.co.uk/thread...ailable-fixed-e-tickets-now-available.192080/
I have also just noticed that the Grand Central website actually says previous versions of Grand Central e-tickets were provided as PDFs which could be printed or shown on your phone. So it would appear that GC has actually switched from offering proper e-tickets to offering m-tickets or print-at-home-tickets, which is the opposite of what many other operators have done.
It would appear that CrossCountry offers e-tickets if you book via their website or m-tickets if you book via their app.