Automated Letter Writing System

I need a streamlined way to draft professional-quality letters and have them dispatched automatically without my constant intervention. At the moment I create every document from scratch, copy-paste details, and manually send each one—an error-prone and time-consuming routine I want to eliminate.

Here is what I’m after:
• A set of reusable letter templates that can pull recipient data (name, address, dates, figures, custom paragraphs) from a simple spreadsheet or database.
• An automation script or lightweight application that merges those templates with live data, generates a ready-to-send file for each recipient, and then sends or exports it in the appropriate format.
• A quick way for me to tweak wording or add a new template without touching code every time.
• Clear instructions so that anyone on my team can run the process after hand-off.

You’re free to choose the most efficient stack—Python, Google Apps Script, Zapier, or any similar tool—so long as the final workflow is reliable and easy to maintain. Let me know what additional details you’d need from my side and how you would approach testing to be sure every letter reaches the right person with the right information.