Help! Need resources that outline standard IT security practices, especially for email

I am a new google workspace administrator for my local civic association. The association has been using google workspace for some time. I am trying to step up IT security for the association, and am receiving a lot of pushback, specifically around the use of external emails.

Several board members use external emails for association business. I am trying to get everyone to use their domain emails.

I already sent the board a detailed email why its important to use …

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