Phplist is one of the best open sources mailing list program out there. However the configuration sometimes may put a few users off.
Here is my email throttle settings of PHPLIST, that should work for you also if you are hosted with bluehost.
Essentially it’s sending 120 mails every 300 seconds. This way it can’t send more than 1,200 email an hour. They give you 1,500 Emails per hour for Pro accounts and 150 for Basic Account
If you are on The basic hosting, you can use a Batch_period of 3600. It’s always better to keep a few relays of your regular emails so don’t let the system send the maximum number of emails allowed per hour.
If you exceed the limit you start getting “could not instantiate mail function”