Hello gliders,
I’m working on a new app that has a Job List and I need to communicate with all registered users when a new job post is done. The customer requested it to be via email. At the same time, the customer does not want to pay for an extra tool or wants to pay a very low fee to it. 
I know there are a lot of transactional mail services but I’m not clear what of those can fit better.
As information, we have around 3.000 registered users.
It sucks when you have 3000 users and the client doesn’t want to pay to send the email. It won’t be easy to send to 3000 at once, you might run into trouble with Google for doing something like that.
SendGrid might be an option for you, but each email can only include up to 1000 recipients (that’s a number to show that 3000 is not a small number at all, and the client should pay).
if the email body is the same, you can use BCC and add, up to 500 recipients per email (depending on the size of the text) which would give you up to 50k for a free account and up to 750k for a G-Suite account… I have never tried it so, I can’t guarantee that 
… but 3,000 will be not a problem, that I’m positive.