Britec Tech Support Forum

Read this especially the part about 'recovering deleted emails from server';

https://support.office.com/en-gb/article/Recover-deleted-items-in-Outlook-for-Windows-49e81f3c-c8f4-4426-a0b9-c0fd751d48ce

Who hosts your email server? there should be a copy of the emails on the server. When you open Outlook 2016 it downloads emails from your server but leaves a copy up on the server unless you set it to delete copies on the server once downloaded.