TL;DR
Email bounce rate is the percentage of sent emails that are returned undelivered — either permanently (hard bounce: invalid address) or temporarily (soft bounce: full inbox, server timeout). Hard bounce rate above 2% starts damaging domain reputation; above 5% triggers active spam filtering. Top cold email teams maintain hard bounce rates below 1% by verifying lists before sending (Mailchimp Email Benchmarks 2024; Validity Benchmark Report 2024).
What is email bounce rate?
Email bounce rate is the percentage of sent emails that are returned to the sender as undeliverable — split into two types. Hard bounces are permanent failures: the email address doesn't exist, the domain is invalid, or the recipient's mail server has blocked the sender. Soft bounces are temporary failures: the recipient's inbox is full, the receiving server is temporarily down, or the message exceeded size limits.
For cold email senders, hard bounce rate is the number that matters. Every hard bounce is a signal to receiving ISPs that the sender is emailing invalid addresses — which suggests either list scraping, list purchasing, or careless list management. Any of these patterns correlate strongly with spam, so ISPs penalize high hard bounce rates by routing future emails from that domain to spam or rejecting them outright.
A 2% hard bounce rate sounds small. On a list of 1,000 contacts, it's 20 bounces. On a list of 10,000 over a month, it's 200 bounces — enough to meaningfully damage a domain's sender score and reputation.
Hard bounce vs soft bounce: what each means
Hard and soft bounces have different causes, different implications for the sender, and different required actions.
- Hard bounce: permanent delivery failure. Causes: invalid email address (typo, deleted account, domain no longer exists), mail server actively blocking the sender IP or domain. Action: remove from list immediately. Never retry a hard-bounced address. Each retry is another bounce against your sending reputation.
- Soft bounce: temporary delivery failure. Causes: recipient's inbox is full, receiving mail server is temporarily down, message too large, send limit exceeded by recipient's server. Action: retry after 24–48 hours. Most email sending platforms automatically retry soft bounces 3–5 times before treating them as permanent. If a soft bounce persists for 5+ retries, remove from list.
- SMTP error codes identify which type has occurred. 5xx codes are permanent (hard bounce). 4xx codes are temporary (soft bounce). Most email sending tools track and report these automatically.
How to keep bounce rate below 2%
1. Verify email addresses before sending. Use email verification tools — NeverBounce, ZeroBounce, Hunter.io's email verifier, or Clearbit's email API — to check addresses before they enter any sequence. Verification removes known-invalid addresses, catch-all addresses (high risk), and disposable addresses. A verified list entering cold outreach has a hard bounce rate below 0.5% on day 1.
2. Never use unverified purchased lists. Purchased email lists have 10–30% invalid address rates and often contain spam traps. Any purchased list requires full verification before the first send.
3. Remove hard bounces immediately. Most sending platforms do this automatically. If yours doesn't, build a suppression list and prevent any hard-bounced address from re-entering any sequence.
4. Monitor bounce rate per campaign, not just in aggregate. A campaign targeting a specific list or segment with 8% bounce rate tells you that list has a data quality problem. Aggregate bounce rate of 1.5% can mask individual campaigns with much higher rates.
5. Re-verify lists older than 6 months. Email addresses decay — people leave companies, change roles, abandon addresses. A list built 12 months ago may have 5–8% invalid addresses by now. Re-verify before reactivating dormant lists.
Bounce rate and Gangly outreach
Gangly's Signal Detection surfaces warm accounts based on real-time signals — new hires, funding rounds, company events. These signal-sourced contacts are typically verified against the signal source (LinkedIn profile, company news) and are recent enough to reduce invalid address risk compared to aged static lists. A rep outreaching to a VP who just joined a company three weeks ago has a much lower chance of bouncing than one emailing a list of contacts scraped 18 months ago.
For any list-based outreach through Gangly, verify email addresses with an external tool before connecting the sequence. Gangly's Workflow Sequencer tracks which sends bounced and flags them for removal — preventing repeat bounces from the same address.
See how Outreach Writer works →
At a glance
- Category
- Outreach
- Related
- 5 terms
Frequently asked questions
What is a good bounce rate for cold email?
Under 2% hard bounce rate is the industry standard target. Under 1% is the goal for high-volume cold outbound teams who verify lists aggressively. Above 3% starts degrading domain reputation. Above 5% causes active spam filtering by major ISPs. Soft bounces are less critical — under 5% is normal; most email platforms retry automatically.
What causes a high email bounce rate?
Invalid email addresses (typos, deleted accounts, wrong domains), outdated lists (contacts who changed companies or roles), unverified purchased lists (10–30% invalid address rates), and domain or IP blocks from the receiving server. Fix in this order: verify the list, remove hard bounces, stop using unverified purchased data, and check if your sending IP/domain is blacklisted.
Does bounce rate affect spam filtering?
Yes, directly. Every hard bounce signals to ISPs that the sender is emailing invalid addresses — a pattern associated with spammers who harvest or purchase email lists. Above 2%, ISPs start treating the sending domain with more suspicion. Above 5%, routing to spam or rejection increases measurably. Keep a suppression list of hard-bounced addresses to prevent retries.
How do you reduce bounce rate before a campaign?
Verify every email address with NeverBounce, ZeroBounce, or Hunter.io before the sequence runs. Verification checks addresses against known-invalid databases, catch-all server configurations, and disposable address services. A clean pass takes a few minutes per list and costs $0.01–$0.02 per email. Worth it every time — the cost of one bounce spike to domain reputation far exceeds the verification cost.
What's the difference between bounce rate and spam complaint rate?
Bounce rate is the percentage of emails that fail to deliver (server-level rejection). Spam complaint rate is the percentage of delivered emails that recipients actively mark as spam. Both damage domain reputation, but spam complaints are weighted more heavily by inbox providers. A 2% bounce rate is a data quality problem; a 0.3% spam complaint rate is a targeting or messaging problem.
See it in the product
Bounce rate (email) — in a real Gangly workflow.
Start your 14-day free trial. First workflow live in 5 minutes.