I used to access my talktalk mail from IOS, Android phone and on my Windows 10 computer, Outlook 2010. If I had any issues I used the web verison with IE. Messages older than 2 weeks always dissapered from phone and IOS. Not a big problem, I could see them on computer becuase they were stored in a pst file. I now have a new computer with Outlook 2016. No pst file and its annoying that I lose all access to incoming messages after a couple of weeks. They are even gone from the web version apparently. All connections are IMAP (993). I have a second talk talk e-mail account and set up to forward all messages to that account when recieved on this one. It is not accessed from android or IOS. They seem to survive Ok (for the last month anyway). My wife has a talktalk account too and she does not suffer from the same problems when connecting to Android and IOS too, she can see mail going back years on all devices. My e-mail account is a very old one. It got made into capital letters by an upgrade talktalk did years ago. Should I delete that e-mail account and then hope to set up a new one with the same name, or is there a better fix please? The account in question is the one I used for the forum.
Have you ever considered using an email provider other than Talktalk? I know that it's a bit more work than just continuing to use Talktalk's email servers but it's just a thought. You might want to do a general Google search on the viability of using the email services of any ISP (hint, hint). I'm sure Talktalk do the best they can possibly do to give their cusomers the best possible experience with the email service they supply, but there are always other options.
: - )
After I posted this I went and checked all my devices again. It turned out that one old computer I used infrequently was still downloading e-mails from my acccount and used the POP server. Buried in its settings was a tick against "delete from server after 14 days". Because I ony fired up that computer infrequently the deletions appeared almost random. I have now unchecked that box and the mails no longer disappear from the IMAP server. I can only assume that at some point talktalk decided to synch the POP and IMAP servers and the synching is allowing messages deleted from POP to then delete the same message from IMAP. That must have been a change because I'm sure this POP setting had remained unchanged for (10?) years and yet the IMAP behaviour changed only a few years back. Just a pity it has taken me so long to work out was was happening. Better late than never. A utllity to see all devices acessing the server might have helped (but possibly not if it missed off those conected via the POP server).
There's only one mailbox. The same mailbox is seen in webmail and you can send commands to that mailbox via POP3 or IMAP protocols.
You've just experienced what happens if you use multiple devices not all using IMAP. With IMAP all devices sync to the mailbox and therefore, when synced all see the same mailbox and related folders on the mail server.
It'll certainly be interesting to see if the promised improved security of the new TalkTalk Mail offers two-factor authentication (TFA) that identifies devices signing in to TalkTalk Mail. I use TFA for an external email account and that identifies to me the device operating system and location. Very useful to prevent unauthorised access at the minimal overhead of a fragment in time taken to authorise.