Webmail access has not changed in any way. If the user cannot sign in because there's an error message "Incorrect password" and the password recovery options are no longer available then TalkTalk Support will need to verify you as the registered user and set up new password recovery Reset details.
I'll let TalkTalk know that the password recovery options aren't available. A TalkTalk Support member will need to verify the registered email user, I assume that's you as the account holder, and set up your password recovery alternate email address and mobile number (the Reset details) so you can send a password reset link or code to authenticate a password change.
Prepare for TalkTalk Support - include in the Community Profile (not in these public posts):
Account holder name, TalkTalk home 'phone number (if not Data Only broadband)
Alternative mobile contact number. Full address with postcode (in the Location box)
Scroll down to Private notes to add the email address needing recovery
Check and Save changes
Select here: Update your profile
A TalkTalk Support member will reply to this thread and then Community Private Message you to confirm your customer account details and or details related to the original registration of the email address.
When verified the Reset details will be set up during a working week within 24 hours allowing you to set your own password via the Forgotten your password journey. Make sure the password is ultra-strong and unique to the mailbox. Check via the TalkTalk Mail sign in that you can access the mailbox.
Let us know if you need more guidance.
