You will say it only twice

[#1]

Just now on one of my aa inbox have received over a hundred emails from various sources, all of which I recognise as having delivered, read and deleted, They are dated from 12th onwards. A similar thing has happened with user@user but with a much reduced volume.
What the heck is going on?
Edit
Even more "what the heck"...... the same messages have downloaded again to my aa inbox, and user@user

[#2]

AA inbox?
B.

[#3]

It looks like your POP3 client is not completing the message download transaction. This leads to downloaded messages not being purged from the mail server, so the next time you do a download you get them again.

[#4]

@ Barry Zubel  The Thunderbird in box for the account AA which I created (i.e. aa@username.plus.com)
@spraxyt  Yes,  you are right in your forecast. They've downloaded for a third time.
The problem to be answered is how can the problem be solved? Is it something changed in my settings? I ain't done nowt, except set up username@username to be delivered to Thunderbird's Local Folders ( used for rag bag stuff that does not belong to a separate account like aa@username). That should not affect other accounts/inboxes. My other accounts/in boxes are working OK.

[#5]

I don't suppose you have "Leave messages on server" ticked in the setup for that account, do you?
B.

[#6]

Either that or try deleting the emails in webmai and see how it behaves in the future.

[#7]

@ Barry Zubel.  I set up the account some time ago and have never touched the server settings since then. I am utterly puzzled why this has not happened before. But your informed guess is proven correct. I have unchecked box and will see the result. Thanks.

[#8]

What has happened is that your mail client "remembers" which messages have been left on the server.  Occasionally, your mail software becomes a little forgetful and confused over which messages it has seen before, and tries to download them all again!
In normal operation, you shouldn't be leaving messages on the server anyway, so this should solve it (and probably make mail retrieval somewhat faster in the future!)
B.

[#9]

@ Barry Z As I said above I do not recall changing any setting recently, so am puzzled, and all the more as even though I reset just now not to leave messages 76 of the 100+ have downloaded again.
@JamesEH Only the username@username items come through ( or used to) to webmail in box. I'm thick,  so I cannot see how to get the other accounts there, were I to want to.

[#10]

I use Thunderbird with SMPT to sort out if any are in the wrong box, i.e. my wife uses two boxes on one laptop, and I use another five.  We then download using Pop3 and OE.  if I forget to compact the server folders, I get two copies of the ones that I have moved, or a copy of the ones that I have deleted, dont know how long they stay hidden on the server but they certainly do

[#11]

Quote from: lucerne

@JamesEH Only the username@username items come through ( or used to) to webmail in box. I'm thick,  so I cannot see how to get the other accounts there, were I to want to.

I assume the username mailbox is the one that (not surprisingly) goes with your username. To see any other mailboxes you need to log into them specifically with username+mailboxname (not forgetting the "+") in the webmail "Name" field and mailboxname's password in the "Password" box.

[#12]

Quote from: pierre_pierre

I use Thunderbird with SMPT to sort out if any are in the wrong box, .......

I'm lost with that  

[#13]

I suspect he probably meant IMAP.

[#14]

yes sorry