Recently I reinstalled Windows 10 on my computer and on top of Windows, I installed Microsoft Office 2016.
When I setup my email on Outlook 2016, I noticed that only part of my emails which is on my Exchange mailbox had synchronized with my Outlook. This was not the case before where all my mails use to synch and due to this the search operations especially on older emails were a bit slow.
After some research I found out its due to the fact that Outlook has a behavior where it limits the emails to be synched considering the hard disk space when you are setting up a cached Exchange mode mailbox.
In order to increase this;
Open Outlook => File => drop down Account settings => select Account settings => Under email select the email account and click on change.
Move the slider according to the timeline you require and click next and finish.
Once done, your emails will start to synch and download.