If your script does not do any throttling, then an email list of 120 would be under the per hour limit, but since the program may send all the emails at one time you are going to run into the per minute limit.

Some people will send out email from their email clients in batches of 20 each, which may take a while to do if you have a large mailing list.

What I generally recommend, although it involves a little work to get everything setup:

1. Install phplist to your site.
2. Setup phplist where users can not email back to it (not sure how exactly this would be done, would have to review possible settings)
3. Put your complete mailing list into phplist
4. Set the throttle to 4 emails per minute, which will do 240 per hour, giving you some "leeway" for any other scripts you have that send email, and for regular email sending.
5. You can then be the only one allowed to "send" to the mailing list.

Doing the above will allow you to stay within the email mailing limits and would only require you to send one email to the mailing list which would then send out to each person on the mailing list, at the throttling limit you set up.

If you have users who are going to be replying to the emails you send out, I would recommend skipping steps 2 and 5, but set the mailing list where you have to "moderate" all replies.   You can then go in and see the replies without having them go to everyone, and then separately email the users in your regular mail client if needed.

Just stick inside the while (or do while) loop you use. That'll throttle you down to 20 per min. Increase it to 7 or 8 if you want to make sure you're under 20 per min.