how to fix outlook 2016 not syncing mail folders with telstra webmail

Hi Rod Prior,

Thank you for clarifying. If the missing messages are still available in Outlook but not in Telstra Webmail, please do not clear the offline items, rebuild the cache, remove the old POP account, or delete any Outlook data files yet. Those messages may be stored only on the computer, and resetting the local data could remove the only accessible copy.

First, back up the affected folders by exporting them to an Outlook Data File (.pst) through File > Open & Export > Import/Export > Export to a file > Outlook Data File (.pst). Make sure Include subfolders is selected, then confirm that the exported file can be opened before making further changes.

After the backup is secured, right-click the Telstra IMAP account in the folder pane, select IMAP Folders > Query, and subscribe to any missing server folders. You can also select Update Folder List. If the old POP messages still do not appear in Telstra Webmail, they will need to be copied from the old local Outlook folders into the corresponding IMAP folders, preferably in small batches, and then checked in Webmail.

Please also clarify whether the missing items are currently visible in Outlook but absent from Telstra Webmail, or visible in Webmail but absent from Outlook, as the correct next step depends on where the remaining copy is stored. Thank you so much for your understanding.   

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Cant use the answer as I will lose the data missing from WEBMAIL