Recently we came across email block with the type "Mail rate exceeded limit".

Here is our set up and usage, in brief:

1. We are sending emails which are transactional in nature and a user explicitly triggers it after providing his/her email id. [email verification, recover password, and user registration trace mail to internal user]

2. We send these using a mobile app 

3. DKIM and SPF are set rightly. There doesn't seem to be any other issue in the setup.

4.  The volume of mail at present is approx 30 max per day. We are expecting it to grow few hundreds once we launch the app in production.

5. We are not sending any email for digital marketing purpose.

I would like to ascertain if we are using right email solution since we are expecting volume to grow and don't wish our users to face lack of emails.

Thanks,