Well, I've had a positive experience - my transfer to Greenby email! 🤣
(You don't hear that often!).
Apart from a couple of initial 'glitches' it seems to be going OK. As I use the webmail client the newer version of Roundcube that Greenby use seems an improvement over the old Plusnet one. Specifically, it works well on a phone as well as a PC.
I hope I haven't tempted the fates by posting this...