To enable/disable this setting requires your NetSuite Administrator to navigate to Setup-Company-General Preferences and then scroll down to Custom Preferences where they will see the setting below. Check/uncheck the 'Attach Gmail to Contact Company' as desired.
What does it do?
Selecting this option will enable all mails attached to contact records to also be attached to customer record. This setting is common to both Native NetSuite communication messages as well as Gmail messages. For example, attaching an email to Contact Joe at company ABC with this setting disabled will not place a copy of the email on the Contact Communication tab, Gmail tab, and on the parent Communication tab. Enabling this setting places a copy of the email on the parent Gmail tab & NetSuite communication tab as well.