Difference Between Hard and Soft Email Bounces (With Examples)

Ever sent a cold email and wondered why it bounced right back, or worse, just disappeared into the void?

I’ve been there, staring at confusing bounce messages and feeling that mix of frustration and “what now?” When I built Reachkit, I learned fast that understanding the difference between hard and soft email bounces is the secret sauce for better deliverability and more booked calls.

In this guide, I’ll break down the real causes behind each bounce type, share examples from my own outreach campaigns, and show you how to keep your sender reputation squeaky clean in 2025. If you want your cold emails to actually land in inboxes (not spam), stick around.

What Are Email Bounces?

If you’ve ever sent a cold email and got a weird “undeliverable” message back, you’ve seen an email bounce in action. An email bounce happens when your message can’t reach the recipient’s inbox, usually because of a problem with the email address or the receiving server. In my experience building Reachkit, bounces are more than just annoying, they can tank your sender reputation and make future emails land in spam.

There are two main email bounce types: hard bounces and soft bounces. Hard bounces mean permanent failure, like an invalid email address. Soft bounces are temporary, like a full inbox. Your bounce rate matters a lot. High bounce rates hurt deliverability and make it harder to book calls. Want the full scoop? Check out my Email Bounces: Everything You Need to Know (2025 Guide).

Hard Email Bounces: Definition and Examples

A hard bounce is when your cold email can’t be delivered, ever. It’s a permanent failure, not just a temporary hiccup. Usually, this happens because the email address is invalid or the domain doesn’t exist.

Here are some classic hard bounce error messages I’ve seen:

• “550 5.1.1 Recipient address rejected: User unknown”
• “No such user here”
• “Domain not found”

When I first started Reachkit, I learned the hard way that too many hard bounces can wreck your sender reputation. If you keep sending to bad addresses, your emails start landing in spam. Always verify emails before hitting send.

Soft Email Bounces: Definition and Examples

A soft email bounce is what happens when your cold email can’t reach a prospect’s inbox because of a temporary problem. It’s not a dead end, just a speed bump. I’ve seen this a lot at Reachkit, especially when sending big B2B campaigns.

Common reasons for soft bounces include:

• The recipient’s inbox is full
• Their email server is down or busy
• Your message is too large

You might see error messages like “Mailbox full,” “Message size exceeds limit,” or “Temporary server error.” Most email tools will try to resend these emails a few times before giving up. If you see repeated soft bounces, it’s a sign to pause and clean your list or tweak your approach.

Key Differences Between Hard and Soft Email Bounces

When it comes to cold email outreach, the difference between hard and soft email bounces can make or break your sender reputation. Hard bounces are permanent failures, like emailing an address that doesn’t exist. Soft bounces are temporary, maybe the recipient’s inbox is full or their server is down.

Here’s how I handle them at Reachkit:

• Hard bounces: Add these emails to your sending blocklist right away. Keeping them tanks your reputation and kills deliverability.
• Soft bounces: Wait and try again later. If they keep bouncing, then remove them.

I learned the hard way that ignoring bounce types leads to wasted effort and fewer booked calls. Here’s a quick comparison:

8 Common Causes of Cold Email Bounces

Cold email bounces can be a real pain, especially when you’re hustling for B2B leads. After building Reachkit and watching thousands of campaigns, I’ve seen the same mistakes trip up even the best sales teams. Here are the eight most common causes of cold email bounces, plus what I wish I’d known sooner:

1. Bad Email List Quality
This is the number one killer. If your list is full of invalid email addresses, typos, or outdated contacts, you’ll see a spike in hard bounces. Always verify your list before hitting send. I once imported a list from an old CRM and watched my bounce rate explode. Lesson learned: clean your list, every time.

2. Sending to Nonexistent Domains
Sometimes, domains just don’t exist anymore. Maybe the company shut down or rebranded. Sending to these addresses leads to permanent email failure. Use email verification tools to catch these before you send.

3. Full Inboxes
Soft bounces often happen when a recipient’s inbox is full. This is more common than you’d think, especially with small businesses. If you see repeated soft bounces, consider removing those contacts after a few tries.

4. Email Server Issues
Temporary server problems on the recipient’s end can cause soft bounces. These are usually out of your control, but if you notice a pattern with certain domains, it might be worth pausing outreach to them for a bit.

5. Poor Email Authentication
If your SPF, DKIM, or DMARC records aren’t set up right, your emails might get blocked or flagged as suspicious. This kills your sender reputation and can lead to both hard and soft bounces. I’ve seen domains get completely blacklisted because of this. Always double-check your domain records.

6. Spam Filters
Spam filters are ruthless. If your content looks spammy, uses too many links, or has weird formatting, you’ll get bounced. Keep your messaging clear, personal, and avoid trigger words. I once tested a “free money” subject line for fun, never again.

7. Message Size Too Large
Attachments or big images can push your email over the size limit. Most servers reject emails that are too large. Stick to plain text and keep attachments to a minimum.

8. High Sending Volume from New Domains
If you blast out hundreds of emails from a fresh domain, you’ll get flagged. Warm up your inboxes and ramp up volume slowly. At Reachkit, we use inbox rotation and warmup to avoid this rookie mistake.

Tips to Avoid Bounces:

• Clean and verify your list before every campaign
• Set up proper email authentication (SPF, DKIM, DMARC)
• Start slow with new domains and warm up your inboxes
• Write clear, non-spammy content
• Monitor bounce reports and remove problem addresses

If you want a deeper dive, check out my full guide on the 8 Common Causes of Cold Email Bounces. Trust me, fixing these will boost your deliverability, get you more replies, and help you book more calls.

Best Practices for Managing Email Bounces

Managing email bounces in cold outreach is a never-ending game, but it’s one you can win with the right habits. I learned early on at Reachkit that setting up automated bounce handling rules is a lifesaver. It keeps your sender reputation clean and your team focused on real prospects, not chasing ghosts.

Make sure you’re monitoring sender reputation and feedback loops. If you ignore those, you’ll end up in spam faster than you can say “full inbox.” I always educate my team on the difference between hard and soft email bounces, so they know how to respond and when to remove an invalid email address.

Stay sharp by following email deliverability trends in 2025. The rules change fast, and what worked last year might tank your campaigns now.

Want to learn more? Check out my guide on why your emails keep bouncing back.

Conclusion

Understanding the difference between hard and soft email bounces is a game-changer for cold email outreach.

When you know what’s really blocking your emails, you can fix issues fast, protect your sender reputation, and actually get your messages in front of real prospects. That’s how you build predictable, scalable revenue instead of just hoping for replies.

Ready to stop guessing and start landing in the inbox? Start your free Reachkit trial below and let’s make your next campaign your best yet.