Gmail has it is own way to store the received emails  is now a little tricky and getting a little complicated for the average normal employees to handle. But the simplest way for the employee to check their GMAIL is to :

1. First, Check the junk folder

2. Using the Gmail APP , the user is adviced to check the  [ All mail], [Important] ,

        [Starred] & [Updates] folders.  see below image

    

Gmail Labels and Folders

Sometimes and based on Gmail internal algorithm and based on employee settings, Gmail would store the received emails into the different labels or folders within the Gmail account such as [Starred] [ Important] [Social] [Updates] [forums] [Promotions]….etc

Accessing Gmail from the mobile can get more difficult at some stages and depends on how the employees installed and configured their Gmail accounts.

There are many configurations that affect how Gmail can  Sync the different Folders and displaying notifications on the mobile app for the received emails.

Please find below a Help article from Google about Sync and Not receiving email Issues and how to solve it

Fix sync errors with the Gmail Android app

Not receiving email from sender