After a lot of trial and error testing, I found the same function has now been remapped to swiping three fingers left or right. Don't know why this changed, but am happy that I do not have to shift between the trackpad and keyboard to read my mails.
Also pressing 'Space' takes you to the next message.
[crarko adds: What I found is that pressing the Spacebar will scroll down by pages in the current message, and then when the end is reached progress on to the next message.]

