Slow download of emails to MS Outlook client via POP3 (follow on from closed discussion)

[#1]

This is a follow-up to discussion
https://community.plus.net/t5/ADSL-Broadband/POP3-emails-throttled-on-PlusNet-broadband-affects-both...
which was closed with only a work-around and no solution.  I didn't know how to get it reopened.

As several people, including @Townman, @Kelly, @jab1 and @bobpullen tried to help me on this, I thought it right to relate recent findings.  Best read quickly through the original discussion first…

(Welcome back.)  As mentioned therein, after I had read some other discussions and gone up the false trail of ‘DNS spoofing’, I had found I could cure the problem of slow (POP3) mail delivery to Outlook by specifying the DSN address(es) explicitly in my computer (IPv4 properties), in place of the more normal ‘automatic’ setting which leaves the router to dictate the DNS address(es) according to its internal settings.  I initially specified Google DNS servers [8.8.8.8.(primary) and 8.8.4.4 (alternate)], and I later changed to use PlusNet's own ones 212.159.13.49 and 212.159.13.50.  Both sets worked, causing email delivery speed to return to normal speed – to my great relief – but it remained a mystery as to why, given that the router-determined DNS addresses previously in use would (I assumed) have been the self-same DNS addresses as above.  Well, that assumption was wrong.

I recently took the blindingly obvious step (for unconnected reasons, to be honest) of checking just what DNS addresses my router is configured to use.  It turns out these are not the standard Plusnet ones mentioned above, nor the further pair that PlusNet give (212.159.6.9 and 212.159.6.10), but 213.20.234.42 and 213.20.234.38.  These, I now find, are the ones for use in connection with PlusNet Safeguard.

Rusty wheels turn in my cranium and I recall now that around the time that I raised the original discussion, I had set up Plusnet Safeguard at a friend’s behest, in order that his two very bright boys would not be able to browse inappropriate web content while in our care.  PN Safeguard apparently (after activation with a router reboot) causes the router’s configured DNS addresses to be changed to these special ones.  [Of course, the noble safeguarding endeavour was, I presume, then undermined by my subsequent DNS override on the computer, but there we are.]

So that explains the changed behaviour upon setting the DNS override up, and I apologise for anyone’s time being wasted over it.  Some questions remain, however:

1. Why were emails downloading so slowly to Outlook when the PN Safeguard DNS servers were being used? Does Safeguard also peruse email content (e.g. for links to unwanted sites) as well as simply stopping web-browsing to such sites?  (I don’t think it does.)  Or is it some quirk of how Outlook is (or was -- see below) connecting to mail servers?
   
   
2. At some later point I appear to have dropped the DNS override setting anyway on my computer (i.e. gone back to letting my router decide) – which means it was from then on using the Safeguard DNS servers again. I have no memory of doing that – it may have happened in a system upgrade, or perhaps because I had been testing to see if the slow delivery problem was still going on and forgot to set it back afterwards – but the original problem evidently ‘went away’, as my emails have been coming down at normal speed with the Safeguard DNS servers in use. Maybe an Outlook update cured it at some stage?
   [That’s the trouble with Office 365 (now Microsoft 365): you don’t know when updates are being applied, as they go in willy-nilly.  But even if I had seen the relevant upgrade come in, I would not have known what exactly what had been done to fix the problem.  This annoys me, but at least the problem is gone.
   
   
3. Why didn’t anyone tell me to check the router DNS settings (the bleeding obvious)? You are all too polite.
   
   
4. Why was this never a problem in Outlook on my wife’s machine, which was on the same releases of Office and Windows 10 as I had on my machine?
   
   
5. Why was other download traffic such as web-browsing and data downloads never slowed? It does seem to have been solely related to emails being read via POP3 into Outlook client (and not just from PlusNet’s email servers).

I don’t expect I’ll ever know the answer to most of these.  Thanks for help previously given.  At least part of the mystery was eventually solved.

[#2]

To answer this one:-

Does Safeguard also peruse email content (e.g. for links to unwanted sites) as well as simply stopping web-browsing to such sites? (I don’t think it does.) 

Safeguard concerns itself with DNS resolution, not email content. A lookup to the Plusnet POP3 server - mail.plus.net - would be referred to the Safeguard DNS servers, but assuming it is not on any block list (which it wouldn't be), then the servers would just reply with the IP address of the mail server.

As to why it caused you problems, I doubt we'll ever get to the bottom of that if it is no longer happening.