All,

Please make sure to put a cover sheet on your TPS reports.

Team,

Please make sure to put a cover sheet on your TPS reports.

Everyone,

Please make sure to put a cover sheet on your TPS reports.

Good Afternoon/Morning,

Please make sure to put a cover sheet on your TPS reports.

Staff,

Please make sure to put a cover sheet on your TPS reports.

I just quickly browsed through my emails I've received this year (coworkers, customers, vendors) and that covers all the ones I've received. All of those are perfectly acceptable.

I wouldn't be personally use "guys," "gals," or "guys and gals" in a non-friend situation.