Hi Ivy,
Where did you install version 13.x? Did you follow the steps in the linked article? When doing a major upgrade you need to stop the SmarterMail service and uninstall the previous version first; your mail data would not be deleted.
If you're not sure what the steps in the linked article are referring to, it might be that you're receiving SmarterMail as a hosted service and don't actually manage the installation. An upgrade can only be done by someone who has access to the server SmarterMail is installed on.
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