I have recently gone through an informative article that explains the top 5 techniques that will help in troubleshooting why Gmail is not receiving emails. In this article, you will also find the various reasons that cause this problem. If you have encountered with this problem then you can refer to this article which clearly explains the following 5 troubleshooting methods.
Check Gmail’s server status
Checking the Gmail Storage
Delete Email Filters
Turn Off Email Forwarding
Temporarily Disable Antivirus or Firewalls
These are the top 5 methods that you can try however, it is advisable to regularly backup your Gmail data so that you can optimize its free storage space. You can achieve this by using reliable Gmail Backup Software which will allow you to back up and migrate your Gmail emails into various file formats and email clients.