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User is deactivated usually means that the mailbox no longer exists. You can check if this is true by verifying the email address at Verifalia.com. If that returns an 'Undeliverable' response then that confirms the mailbox cannot be found on the TalkTalk Mail platform. The mailbox is then either deleted or suspended for security reasons. If suspended then a password change is required.
The Reset password now button in the help article Changing your email password will take you to password reset and recovery.
If the email address is still active on the TalkTalk Mail platform and you have set up password recovery options, in advance, that you recognise from the *****hints, then you can send your alternate email address a link or your mobile a 6-digit code to authorise a password reset.
