I know someone work as MIS support. He said once he was helping a HR Manager to solve a problem when the HR Manager couldn't receive any email for the past one week.
So he went to her company, log in to Gmail using her PC to send a test email to her Outlook and also her secretary's email. And true enough only her secretary receive the test email but not the HR Manager. This shows no problem on the office networking.
Only seconds later, he found the root cause of the problem. The HR Manager's mail in Inbox is sorted by date in reversed. A press of the Date Tab, hundreds of unread emails floating the screen.