First check that the mailbox is working via webmail.
Select here: Sign in to TalkTalk Mail
Enter your full TalkTalk Mail tiscali email address, select Continue and enter the tiscali email password, select Sign in.
Does the password meet minimum security requirements? At least 8 characters, although I recommend 12 - 15 characters, and including multicase letters and at least one number and one symbol. A weak password may be rejected by the mail servers that Outlook connects to.
Whilst you're signed in to webmail, select the user icon top right and select the menu item Update your reset details. This is to make sure you do have password recovery options saved just in case you need to upgrade the password.
Which version of Outlook are you using and with what Operating system? For example, Outlook 2019 on Windows 11. There are many versions of Outlook and not all set up the same way.
Take screenshots of the incoming and outgoing server settings, image edit to obscure the first part of the tiscali email address and upload here using the camera icon above this reply area. I'll advise on the settings.
