To help prevent spam and malicious email, add individual email addresses or entire domains to a blocked senders list. This way, you’re automatically rejecting messages from them. 


Kindly follow the steps as mentioned below:

  1. In your Google Admin console(at admin.google.com)...
  2. To apply the setting to everyone, leave the top organizational unit selected. Otherwise, select a child organizational unit.

  3. Point to Blocked senders and choose an option:

    • To edit an existing setting, click Edit.

    • For a new setting, click Configure or Add anotherand thenenter a unique description.

  4. Click Use existing.

  5. To use an existing list as your blocked sender list, under Available lists, click the list name.
  6. Enter one or more IPs. Separate each entry with a comma or space.

  7. Click Save.

  8. Click Add Setting or Save.

    The Gmail Advanced settings page will display new settings.

    1. At the bottom of the page, click Save.
    2. It can take up to 24 hours for changes to take effect. You can track changes in the Admin audit log.


Note:  Be sure to enter public IP4 addresses as private IPs are not accepted. Also, IP4 IP Addresses should be in proper format.