Less than 2% of your sent emails should ever bounce. Cross that line and inbox providers start treating you like a spammer, and anything above 5% is a red flag that can get your account suspended. (Email Bounce Rate Benchmarks by Industry (2026 Data)) I’ve watched a single bad list push a client’s bounce rate past 5% overnight. The sender reputation damage took weeks to undo.

Here’s exactly what soft and hard bounces are, and the 4 steps I use to keep bounces near zero.

Quick note: these tactics are built for cold outbound sending, not bulk newsletter blasts. The sending patterns and thresholds differ.

It’s quite simple:

If your email outreach produces many bounces, internet service providers think you’re a spammer.

Consequently, your email sender reputation gets dealt a blow and your deliverability decreases. Now, you’re getting even more bounces, lowering your sender reputation even more. It’s a snowball effect.

An overall bounce rate below 2% is considered healthy (The Email Bounce Rate Benchmark — How Do You Compare? | ZB), according to ZeroBounce’s benchmark data. Over 2% is considered high, and you need to examine your list hygiene and practices. (The Email Bounce Rate Benchmark — How Do You Compare? | ZB)

Emails bounce due to deliverability problems. There are two types of bounces: soft and hard.

Soft bounces are caused by temporary issues. Hard bounces by permanent ones. The quickest way to tell them apart is by looking at the SMTP reply codes your mail server returns. Codes beginning with 4 signal temporary failures (retry is appropriate), and codes beginning with 5 signal permanent failures (retrying without changes will not help). These are standardized in RFC 5321, which governs the SMTP protocol today. (SMTP Error Codes: 4xx vs 5xx Reference Guide)

A soft bounce means the receiving server rejected your email temporarily. In SMTP terms, that’s a 4xx code, a temporary failure. The client should retry later. Examples: mailbox full (452), server busy (421). (RFC 5321 – Simple Mail Transfer Protocol - Mailer To Go)

Soft bounces may occur when:

The receiving server is saying “not now, try again later.” Most sending servers will automatically retry for up to 72 hours before giving up.

Hard bounces have permanent causes. In SMTP terms, that’s a 5xx code, a permanent failure. Do not retry. Examples: user unknown (550), syntax error (500), relay denied (553). (RFC 5321 – Simple Mail Transfer Protocol - Mailer To Go)

They may occur when:

A 5xx code is a hard rejection. RFC 5321 mandates that 5xx is permanent. Retrying a 5xx bounce violates protocol semantics and damages sender reputation (RFC 5321 SMTP Protocol: Commands, Reply Codes, ESMTP Extensions) because receivers track how many times you send to known-bad addresses.

It’s important to note that a poor sender reputation can cause hard bounces on its own, even when the email address is valid.

One consistent finding across different benchmark studies is that less than 2% of emails bouncing back is a healthy range. 2–5% is a warning level that calls for list hygiene and verification. Above 5% is critical and can seriously damage sender reputation. (Email Bounce Rate Benchmark 2025–2026: By Industry, Hard vs Soft, and How to Reduce It)

For cold outbound specifically, a reasonable benchmark is under 2% total, with hard bounces ideally below 1% (What’s a Good Email Bounce Rate for Paid Data? | Apollo), according to Apollo’s benchmark data. A 2% bounce rate is a widely adopted benchmark in the cold email industry. (1. Cold Email Guide)

In my experience, if you’re consistently above 2%, something in your process is broken. If you’re above 5%, stop sending and fix it before you do more damage.

Eliminating all bounces is close to impossible.

However, most of them can be avoided by following the four steps below.

Before diving into the tooling, though, the basics matter: manually remove hard-bounced addresses from your lists immediately, and give soft bounces time to resolve with a retry backoff before you write them off. No tool replaces that discipline.

Never send to unverified emails.

Unverified emails could be addresses that don’t exist or experience technical problems.

Ensure to verify the emails of your leads before contacting them.

With lemlist’s Email Finder & Verifier, you can verify the emails of all your leads before a single message goes out. It gives you access to 14 best-in-class data providers with a single subscription, with higher find rates, broader coverage, and a fraction of the cost of stacking multiple tools. (lemlist’s Waterfall Enrichment: Find ~80% Verified Leads’ Emails)

lemlist is rated 4.6/5 on G2 from 2,000+ reviews.

Remember, your email list needs to be verified regularly to limit the amount of bounces you’ll get. Lists decay over time. I re-verify any list that’s older than 30 days.

Your sender reputation is your foot in the door, so make sure it doesn’t stink. 😉

I’ve seen reps skip warm-up on a fresh domain and wonder why half their emails bounced on day two. Don’t be that person.

The obvious first step to improving or maintaining your reputation is not sending spammy emails. A good start is to avoid these spam trigger words.

But there’s more…

For new sending domains, it’s important to warm up your email.

You can do so through an email deliverability booster like lemwarm.

Additionally, you must authenticate your sending domain through DNS records if you don’t want to land in spam.

The specific domain authentication records that you need to set up for your domain are:

This one is a no-brainer. ✖️

Why keep sending to an email address that doesn’t work? It only gets you more bounces and further tarnishes your sender reputation.

So, if the first email bounces, stop any scheduled follow-ups immediately.

lemlist stops any scheduled follow-ups automatically the moment an email hard bounces. You don’t have to lift a finger.

Fixing bounces once isn’t enough. Lists decay, domains change, and new leads bring new risk. You need ongoing visibility.

Track bounce trends before they tank your sender reputation with lemlist’s Deliverability Hub, which flags bounce spikes per mailbox and domain automatically. That way you catch a problem at 1.5% instead of discovering it at 5%.

I check my bounce trends weekly. It takes two minutes and has saved me from at least one domain reputation disaster.

Bounces are bad for your deliverability, and hard bounces especially so.

The good news: most bounces are preventable. Verify your lists, warm up your domains, stop follow-ups to dead addresses, and monitor trends over time. Do those four things and you’ll stay well under the 2% threshold.

Start a 14-day free trial and let lemlist’s Deliverability Hub keep your bounce rate in check while you scale outreach.