error 0x004210a

You're right to identify which Outlook you're using, Bernard Gibson, as troubleshooting differs between new and classic Outlook. The differences are:

• Open File > Office Account > About Outlook > this is Classic Outlook and the version/build is shown there.
• If you do not have the File tab but a Settings gear at the top instead, you're likely using new Outlook.

Now, error 0x8004210A means Outlook timed out while waiting for the incoming POP server to respond. Since messages are still reaching TalkTalk Webmail and you have already verified the ports, the issue is likely with Outlook’s POP connection or profile rather than missing emails. This often happens to Classic version:

1 - Make sure Windows and Outlook are fully updated

• Go to Settings > Windows Update > Check for updates
  • Then go to Advanced options > Optional updates
  • Install all available updates and reboot.
• In Outlook, select File > Office Account > Update Options > Update Now.

2 - Repair the account

• In Outlook, select File > Account Settings > Account Settings.
• Select the TalkTalk account > Repair > follow prompts > restart Outlook.

3 - Create a fresh Outlook profile

• Close Outlook completely > open Control Panel > search for Mail.
• Select Mail (Microsoft Outlook) > Show Profiles > Add.
• Add the TalkTalk account and test it before removing the old profile.

If that doesn't resolve it, please let me know your Outlook version and its build. With those details, we can narrow down the next steps rather than changing the server settings that you've already checked.