Mass Mail works fine when I send to all Super Users (3), but NOT when I send to all Registered users (64?). Even when the other setting are the same (BCC on, HTML off, etc...). I'm using Joomla 3.4.8, on SiteGround web hosting.
I've tried both phpmail and sendmail. Both have the same results, just a different error msg:
Notice Could not instantiate mail function
Notice Could not execute: /usr/sbin/sendmail -t -i