Resend SDK v1.0.1 Has Two Breaking Changes That Fail Silently (Here Is the Fix)

My job application pipeline sends emails automatically. Cover letters, follow-ups, confirmations — all automated through a Python script using the Resend SDK. One morning last week, I noticed the email queue was building up but nothing was going out. No errors in the logs. The script was running. The function returned successfully. The emails just... never arrived. After about 30 minutes of debugging, I found the cause: Resend had shipped v1.0.1 of their Python SDK with two silent breaking changes that didn't announce themselves as errors — just silent failures. Here's what broke and how to fix it. The Setup I run an agentic job search system — a collection of Python scripts and cron jobs that manage my pipeline from discovery to application. One component handles all outbound email: job application follow-ups, confirmation pings to myself, outreach emails. The script had been working fine for weeks. Then it stopped. Breaking Change #1: The from Key Got Renamed to sender The original s