Hi, thanks for the suggestion.
No, all my email accounts from other providers are fine, even one on another of the same ISP's servers. Using the same email client, or a different one on my tablet. Have done all the possible end-to-end trials we can with results suggesting it could be my end (local cabinet/Plusnet gateway), or their end (the same slowness is shown not only on email but on file download using cPanel file manager (but ok on direct https) or the backend https configurator of a Wordpress site I run (but not the frontend direct https access), but in the end thwre's no single point of failure obvious.
We've concluded it's something strange about the routing between these two IP addresses. I'm currently getting to grips with Wireshark to see if I can see what's happening. The real-time traffic speed indicator I run shows the traffic is very peaky - constant hunting from 800 to 200 kbps and back with 500 as only an average, and my broadbamd line happily does 40 Mbps on https and other email servers. So it looks like either some dropped packets, lost ACKs, packets with almost nothing in the application layer section of the packet, or some such.
If I get to the bottom of it, I'll post.
