Claude Code email

No Bounce Handling Causing Sender Reputation Damage

Your application continues to send emails to addresses that have previously bounced (invalid addresses, full mailboxes, blocked domains). This damages your sender reputation score, causing email providers to throttle or block all your emails, including those to valid recipients.

Without bounce handling, your deliverability degrades over time. Emails that used to reach inboxes start landing in spam, then stop arriving at all. By the time you notice, your sending domain may be blacklisted and recovery takes weeks.

The issue compounds because every failed delivery attempt further damages your reputation, creating a downward spiral that affects all your users, not just the ones with invalid addresses.

Error Messages You Might See

550 5.1.1 User unknown 552 Mailbox full Email suppressed: previously bounced Sender reputation score: critical Domain blacklisted by Spamhaus
550 5.1.1 User unknown552 Mailbox fullEmail suppressed: previously bouncedSender reputation score: criticalDomain blacklisted by Spamhaus

Common Causes

  • No webhook listener for bounces — The email service reports bounces via webhooks but the app has no endpoint to receive them
  • Bounced addresses not flagged — Even if bounce notifications are received, the app doesn't mark addresses as invalid in the database
  • No distinction between hard and soft bounces — Hard bounces (invalid address) should permanently stop sending, soft bounces (full mailbox) should retry then stop
  • Suppression list not checked before sending — The app doesn't check a suppression list before attempting to send each email
  • Catch-all sending to user-provided addresses — Newsletter or notification features send to any address without validation

How to Fix It

  1. Set up bounce webhook endpoint — Create an endpoint to receive bounce notifications from your email provider (SendGrid Event Webhook, Mailgun webhooks, SES notifications)
  2. Maintain a suppression list — Store bounced addresses in a database table and check it before every send
  3. Handle bounce types differently — Permanently suppress hard bounces immediately. Retry soft bounces 3 times over 72 hours, then suppress
  4. Validate email addresses at signup — Use email verification APIs or double opt-in to prevent invalid addresses from entering your system
  5. Monitor sender reputation — Use tools like Google Postmaster Tools and your email provider's reputation dashboard to track your domain health

Real developers can help you.

Franck Plazanet Franck Plazanet I am a Strategic Engineering Leader with over 8 years of experience building high-availability enterprise systems and scaling high-performing technical teams. My focus is on bridging the gap between complex technology and business growth. Core Expertise: 🚀 Leadership: Managing and coaching teams of 15+ engineers, fostering a culture of accountability and continuous improvement. 🏗️ Architecture: Enterprise Core Systems, Multi-system Integration (ERP/API/ETL), and Core Database Structure. ☁️ Cloud & Scale: AWS Expert; architected systems handling 10B+ monthly requests and managing 100k+ SKUs. 📈 Business Impact: Aligning tech strategy with P&L goals to drive $70k+ in monthly recurring revenue. I thrive on "out-of-the-box" thinking to solve complex technical bottlenecks and am always looking for ways to use automation to improve business productivity. MFox MFox Full-stack professional senior engineer (15+years). Extensive experience in software development, qa, and IP networking. Nam Tran Nam Tran 10 years as fullstack developer Matthew Jordan 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. Jen Jacobsen Jen Jacobsen I’m a Full-Stack Developer with over 10 years of experience building modern web and mobile applications. I enjoy working across the full product lifecycle — turning ideas into real, well-built products that are intuitive for users and scalable for businesses. I particularly enjoy building mobile apps, modern web platforms, and solving complex technical problems in a way that keeps systems clean, reliable, and easy to maintain. Taufan Taufan I’m a product-focused engineer and tech leader who builds scalable systems and turns ideas into production-ready platforms. Over the past years, I’ve worked across startups and fast-moving teams, leading backend architecture, improving system reliability, and shipping products used by thousands of users. My strength is not just writing code — but connecting product vision, technical execution, and business impact. Daniel Vázquez Daniel Vázquez Software Engineer with over 10 years of experience on Startups, Government, big tech industry & consulting. Milan Surelia Milan Surelia Milan Surelia is a Mobile App Developer with 5+ years of experience crafting scalable, cross-platform apps at 7Span and Meticha. At 7Span, he engineers feature-rich Flutter apps with smooth performance and modern UI. As the Co-Founder of Meticha, he builds open-source tools and developer-focused products that solve real-world problems. Expertise: 💡 Developing cross-platform apps using Flutter, Dart, and Jetpack Compose for Android, iOS, and Web. 🖋️ Sharing insights through technical writing, blogging, and open-source contributions. 🤝 Collaborating closely with designers, PMs, and developers to build seamless mobile experiences. Notable Achievements: 🎯 Revamped the Vepaar app into Vepaar Store & CRM with a 2x performance boost and smoother UX. 🚀 Launched Compose101 — a Jetpack Compose starter kit to speed up Android development. 🌟 Open source contributions on Github & StackOverflow for Flutter & Dart 🎖️ Worked on improving app performance and user experience with smart solutions. Milan is always happy to connect, work on new ideas, and explore the latest in technology. David Olverson David Olverson Solo dev shipping production apps with AI-assisted development. I specialize in rescuing broken Lovable/Bolt/Cursor builds and taking them to production. 10+ apps shipped including SaaS CRMs, gaming platforms, real estate tools, and Discord bots. Stack: Next.js 16, TypeScript, Tailwind CSS, FastAPI, PostgreSQL, Prisma. I use Claude Code with 50+ custom skills for rapid delivery. Average turnaround: 2-4 weeks from broken prototype to production. Stanislav Prigodich Stanislav Prigodich 15+ years building iOS and web apps at startups and enterprise companies. I want to use that experience to help builders ship real products - when something breaks, I'm here to fix it.

You don't need to be technical. Just describe what's wrong and a verified developer will handle the rest.

Get Help

Frequently Asked Questions

What's the difference between a hard and soft bounce?

A hard bounce means the address is permanently invalid (user doesn't exist, domain doesn't exist). A soft bounce is temporary (mailbox full, server temporarily down). Stop sending to hard bounces immediately; retry soft bounces a few times before suppressing.

How do I recover a damaged sender reputation?

Stop sending to all bounced and unengaged addresses immediately. Clean your list to only active, confirmed recipients. Start sending low volumes and gradually increase. It typically takes 2-4 weeks for reputation to recover.

Related Claude Code Issues

Can't fix it yourself?
Real developers can help.

You don't need to be technical. Just describe what's wrong and a verified developer will handle the rest.

Get Help