[WTH] A Custom Bulk Email Sender

Hello, I will like to create a bulk email sender using smtp. I will prefer if this can be built using python but any language is fine.
It has to be fast and scalable.
Here is what I need:
I have a list of email accounts that will be in a text file or in a csv file.
I have a list of recipients that will be in another text file.

One email account will be able to send out a maximum of 900 emails so it can be broken down into 300/300/300 or 150/150/150/150/150/150 or 100 receipients 9 times.
Once the first email sends out 900 it moves to the next email and that one also sends out another 900 emails and so on.

The program must work if I have 10 emails and 9000 recipients and also if I have 1000 email accounts and 900000 recipients - it must be scalable.

Note: The emails have to be sent out using BCC part of the email (I have a basic version I can share with you needed)

The smtp to be used is Gmail smtp and I will like this to be delivered in 2-3 days.

The email sent will also include an attachment (an image) in the body of the mail.

Please send me a PM if you are able to work on this. Budget is $100, I can pay using crypto or Paypal.