Please check your outlook settings:
Solutions 1:
File account settings -> account settings from the “account settings” window select the email account Click Change Under Offline settings move the slider to the far right till it reads “all” Click Next Restart outlook
Solutions 2:
Change outlook into online mode instead of cached mode.
File > Account Settings > Account Settings > double click on profile > un-check “use Cached Exchange mode” > next > next > finish