Mass email send and test

Hello!

I'm taking over the development of a contest project. This project requires to send a lot (200K-3M) emails per day. For these purposes, the company is using SendGrid API. But what happened last time is they sent 3m emails at once, SendGrid rejected it, this created an infinity loop, customers started to receive 10-15 same emails, the reputation becomes 0 and so one. I was thinking to use Queuing and Jobs to send some small portions of emails every minute or so so that apocalypse wouldn't happen again. We are using a Pro 700K plan.

I found this answer on the forum that seems to be a solution to my problem. https://laracasts.com/discuss/channels/general-discussion/robust-mass-email-with-mandrill?page=1#reply=103814

My question is - how many and how often should the system send emails to prevent blocking the account and how to test it before going live?

I was thinking to fill the database with dummy records like myemail+test1@gmail.com, myemail+test2@gmail.com and so one, but I'm afraid SendGrid simply blocks me.

And also maybe there is a better solution, like a package so Sendgrid will take care of it.

Thanks in advance!