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This will create a Google Sheet of all the contacts in the GAL
gam print gal todrive
If nothing returned, then the Email Address is not in the GAL.
gam show gal emailmatchpattern <Email Address>
Change on|off as required.
gam all users update user gal on
gam all users_ns update user gal on
Remove a user account from the GAL.
gam update user <User Email Address> gal false