Business Outlook MAC users can't send or receive emails

Hi all, 

my company uses office 365 with Outlook exchange for our E-Mails. 

Since the last outlook update, it seems everyone with a MAC computer cannot send or receive E-Mails, and E-Mails from the marketing department are landing in junk folders. 

Our IT guy doesn't have a solution, and best I can tell, the issue is that the digital certificate and encryption certificate is blank. Could that be the cause? Has anyone had anything like this happen?