How can i create a web-based autoresponder using Python/Django?

So I’ve recieved my first paying client and they’ve just sent me a brief to create a web-based auto responder. The application is to run on a online marketplace similar to Amazon.

The details of the brief are below:

  • Marketplace sellers should be able to send their customers an automated follow up e-mail after order asking for feedback, review etc.

  • The autoresponder should be able to fetch all orders and its details: Name, Last name, Order number, Product Name, Value, EAN

  • The tool should periodically (for example each 6 hours) check if new orders are made and should be included in the follow up auto responder.

  • Vendors can create e-mail templates, which will be sent automatically at the scheduled time after the order is delivered.

  • In this e-mail templates, they can standardize messages, such as: Hi, %Name% %Lastname%, you have ordered %productname% etc….

  • The e-mail templates can be used for all product orders or designed to only be sent to specific products based on the product identification number (ASIN / EAN) - If possible, it would be amazing if the tool uses the own mailbox of the User based on his SMTP-mail servers.

  • The User can define when the E-mail templates should be sent (for example after 3 days after the expected delivery date)

  • The User can create the E-mail templates using a WYSIWYG-editor - A Stripe Payment Gateway should be built to capture recurring payments with iDeal and Bancontact (Dutch and Belgium payment methods).

  • If it’s possible to use the mailbox of the user to send the e-mails, they don’t have to use their own resources. In that case, they want 1 plan per month for unlimited e-mails using a custom mailbox. With the following discounts:

  • If User agrees with a yearly contract, he /she will pay a monthly fee of 19,99€

  • If User agrees with a quarterly contract, he/she will pay a monthly fee of €29,99

  • If users agree with a monthly contract, he /she will pay a monthly fee of €39,99

If anyone has had any experience building something similar how would you approach this?