Email Sending Fails After API Deprecation
Your application's email sending suddenly stopped working. Transactional emails (password resets, order confirmations, verification emails) are no longer being delivered. The email service returns errors about deprecated endpoints, removed API versions, or unsupported authentication methods.
Email service providers regularly deprecate old API versions and authentication methods. Claude Code may have generated code using an older API version that was current at training time but has since been retired. Mandrill, SendGrid v2, Mailgun's legacy endpoints, and AWS SES v1 have all gone through major deprecation cycles.
The failure may be sudden (API version shut down) or gradual (deprecated endpoints returning intermittent errors before full removal).
Error Messages You Might See
Common Causes
- Outdated API version — Code uses SendGrid v2 API instead of v3, or AWS SES v1 instead of v2
- Deprecated authentication method — Using API key in query parameters instead of Authorization header
- Removed SDK version — The installed npm/pip package version is no longer supported and has breaking changes
- Endpoint URL changed — The email service moved to a new base URL and the old one returns 404 or 410 Gone
- SMTP relay disabled — The email service discontinued SMTP relay in favor of API-only sending
How to Fix It
- Check the email service's changelog — Review SendGrid, Mailgun, or your provider's deprecation notices for recent API changes
- Upgrade the SDK — Update to the latest version of your email service's official SDK package
- Migrate to the current API version — Rewrite email sending code to use the latest API endpoints and authentication methods
- Use the official SDK instead of raw HTTP — Replace custom fetch/axios calls with the provider's official library, which stays updated
- Add email sending tests — Create integration tests that actually send to a test address to catch breakages early
Real developers can help you.
Omar Faruk
As a Product Engineer at Klasio, I contributed to end-to-end product development, focusing on scalability, performance, and user experience.
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Richard McSorley
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Matthew Jordan
I've been working at a large software company named Kainos for 2 years, and mainly specialise in Platform Engineering. I regularly enjoy working on software products outside of work, and I'm a huge fan of game development using Unity. I personally enjoy Python & C# in my spare time, but I also specialise in multiple different platform-related technologies from my day job.
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Full-stack engineer with 5 years experience building production web apps using React, Next.js and TypeScript.
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I'm a full-stack developer focused on building practical and scalable web applications. My main experience is with **React, TypeScript, and modern frontend architectures**, where I prioritize clean code, component reusability, and maintainable project structures.
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Kingsley Omage
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Get HelpFrequently Asked Questions
How do I know which API version my code uses?
Check the base URL in your HTTP calls (e.g., api.sendgrid.com/api/ is v2, api.sendgrid.com/v3/ is v3). Also check the package version in package.json or requirements.txt against the provider's documentation.
Will upgrading the SDK break my existing code?
Major version upgrades often have breaking changes in method names and response formats. Read the migration guide from your email provider and update your code to match the new API signatures.