How to make mass changes to multiple constituent record's email status, changing the accepts email field from yes (opt in) to no (opt out).
All of the records will need to first be placed in a group. From the Members tab you can click the "select action" link. A popup window will open and from that drop down you'll want to select the Accepts Email field. Change this to no and save. The records will be changed to opt out or accepts email=no. Note that this will not mark mass opt in constituent records, only opt out.