jelv,
(I know this is not the right place for this, but I don't know where else to go, having failed to get anywhere with it on the MS forum. I still don't know if the following is a Microsoft Outlook software fault or something caused by the PlusNet email software.)
I have exactly the problem you describe, in that my email client (MS Outlook 2016) does forget from time to time which emails it has previously downloaded to my computer and downloads them again (sometimes several times). I had no such problem with previous Outlook versions (Outlook 2003 and earlier ones). It is real pain having to keep deleting the duplicated emails and also to have to take remedial action (when they are many) of going on to the server with Webmail to delete them, to stop the repeated downloading.
[Background: - I use POP3. I have set up Outlook on the PC to leave my emails on the server for a week after they are downloaded to the PC. This gives me a window of at least a week to view them on my smartphone before they disappear from the server. - I have set up Samsung Email app on the phone such that it does not delete emails from the server when I delete them from the phone, thus ensuring that all emails still reach my PC. - IMAP does not suit me, because I want (for my own purposes) the PC to be my permanent repository for my emails and only to see recent emails on the phone. Any that I delete on the phone after processing I do not want to be (sync) deleted at the PC. - I am perfectly happy that emails that have been automatically deleted from the server by Outlook on the PC, or that I have explicitly deleted by logging on to PlusNet Webmail (when it actually *£$%^& works!), are no longer accessible on the phone. end-background]
Do you have any knowledge of how the client (Outlook) keeps track of which emails it has previously downloaded, so as not to download them again, and exactly how it later deletes those that have passed their specified 'keep me' interval? If I knew this, I might get to understand how it sometimes 'forgets', as you put it, and annoyingly downloads them again. It might also help me eliminate PlusNet as the cause of the problem.
Vanessen:
This comment is perhaps too late for your trip, but the set-up that spraxyt, jaread83 and jelv have described would do what you want, I think, and using an email client does work around the problem that PlusNet Webmail seems still to be having. Just be aware that if you use IMAP (which is what you must do if you want your emails to remain on the server), then emails will always be synchronised at all your devices, so deleting at one will delete at all. (This was one of several things that did not suit me, which is why I have used POP3 with modifications as described above.)
Also be aware that once you are away from your home PlusNet router, if you try to use a client (e.g. Outlook) to handle emails, then (as I found when away): (a) you will not be able to send any emails from PlusNet without first configuring the account on the client program such that it signs you on to the server just as when you are receiving emails (not needed when you are on your PlusNet network at home); and (b) PlusNet severely limits how many emails you can send per hour – I found when away that when I tried to send Christmas greetings to a dozen or so friends, PlusNet returned me a failure message treating me as a spammer! I raised a ticket about this and was told it was an anti-spam measure which I had to accept. The only way out was to send separate emails over a period of time.
Using PlusNet WebMail directly was better, as I remember, but then I had to BCC myself in in order to retain any copies I wanted on Outlook. Tedious all round.
If there is a better place to post this, then, like Vanessen, I’d be happy to continue there.
