How do I send out mass email without everyone seeing eachothers email?

Bcc.

In gmail there are 3 boxes on the top on one it says "to:" thats where you usually put the email address then the second box it says "Bcc:" so if you enter all the email addresses there noone wont see to whom else you sent...

Put the list of email addresses in the field labeled "bcc:". (That stands for "blind carbon copy".) Each recipient sees his own email address but nobody else's.