I have five Tiscali email addresses, accessed via Windows Mail. 2 days ago just one of these stopped receiving or sending (unfortunately the most-needed one), with a warning triangle & the same message quoted as by @Marvhead1 - 'We couldn't access this account TalkTalk email. You might need to update your password or give the account permission to sync to this device'. All 5 addresses have the same server settings, & 2 of them share the same password as the problem one. Using 'Fix account' & re-entering the password merely repeats the process. I followed the advice from @Gondola to reset Mail & Calendar, which has had no effect (apart from changing viewing settings). I had already restarted my PC, with no effect.
At one time you could just download messages from the TalkTalk server, but this no longer seems possible (the Webmail versions of my addresses all show warning triangles & empty inboxes).
Interestingly, Thunderbird stopped receiving new emails for this address a few days earlier, which might be related to the most recent Windows updates.
