Hard Bounce vs Soft Bounce: What Each Means and When to Suppress

A hard bounce is an email that can't be delivered for a permanent reason, like an address that doesn't exist. A soft bounce is a temporary failure, like a full inbox or a server that's briefly down. Klaviyo suppresses a hard bounce straight away and a soft bounce after 7 in a row. Hayes Media, an email and SMS retention agency for eCommerce brands, keeps hard bounces suppressed and pulls repeat soft bouncers out before Klaviyo's limit.

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

Both are emails that didn't arrive. The difference is whether the reason will still be true the next time you send.

Klaviyo's help center puts it this way: a hard bounce "occurs when an email cannot be delivered due to a permanent reason," and a soft bounce "is always caused by a temporary reason, such as when a recipient's inbox is full or when their email server is momentarily down."

Hard bounce. The address doesn't exist, was mistyped at signup, or the receiving server refused it on purpose. Klaviyo's suppression article names "a misspelled email address or a deliberate block by the email server" as causes. Sending again won't change the result.

Soft bounce. The address is real, but the message couldn't land this time. Klaviyo's bounce categories include a full mailbox, a temporary auto-reply setup, an error on the recipient's mail server, and a provider refusing your volume. The next send might go through. If it keeps failing, that address is costing you reputation and giving you nothing back.

What does Klaviyo do with each type?

Klaviyo handles both automatically, on different rules. Here's what its help center says happens.

Hard bounces are suppressed on the first one. In Klaviyo's words: "Klaviyo automatically suppresses any email address that hard bounces." A suppressed profile can't receive email marketing "even if they have provided consent and indicated they want to receive emails."

Soft bounces are suppressed after a streak. Klaviyo suppresses an address after 7 consecutive soft bounces. Two details change how that count works: "Only soft bounces within the past 2 years are considered for this count," and "A successful delivery breaks the streak."

Suppressed profiles leave your lists. Once a profile is suppressed for a hard bounce or 7 consecutive soft bounces, Klaviyo says "they will automatically be removed from any lists they are on."

Bounce suppressions stick. A new signup or a consented list upload doesn't lift them. Klaviyo states that "Deliverability suppressions (e.g., those due to hard bounces) are not removed by subscribe actions in order to protect your sender reputation." Approved transactional flow emails can still reach manually suppressed or unsubscribed profiles, "but not to profiles suppressed for bounces or invalid email addresses." So a customer whose address hard bounced won't get an order confirmation from a Klaviyo flow either.

Some addresses are skipped before they bounce for you. Klaviyo flags suspicious emails from hard bounce history across its sending infrastructure, and "An address can be marked suspicious even if it has never hard bounced in your account." Those addresses are skipped automatically.

Why do bounces hurt deliverability?

A bounce tells the inbox provider something about how you collect and keep your list. Klaviyo says a high number of bounces "can have a negative impact on your deliverability rate," and that as your reputation drops, "inbox providers may begin sending your emails to spam rather than to a recipient's inbox."

Gmail and Yahoo say the same in their own guidance. Google's sender guidelines list "Automatically unsubscribe recipients who have multiple bounced messages" as a supported unsubscribe option, and tell senders: "If messages start bouncing or start being deferred, reduce the sending volume until the SMTP error rate decreases." Yahoo's sender page says to "Monitor hard and soft bounces as well as inactive recipients" and to "Remove invalid recipients from your list promptly."

Klaviyo cleans up soft bounces on its own, but only after 7 failed sends in a row. Its own bounce rate article says "each time an email bounces, your deliverability is affected." That's why it suggests pulling chronic soft bouncers out earlier.

How do the Gmail and Yahoo sender rules fit in?

Bounce handling sits next to the rules Gmail and Yahoo set for anyone who mails their users. Read the scope carefully, because Google splits its rules in two.

Gmail, all senders. Google says that starting February 1, 2024, "all email senders who send email to Gmail accounts must meet the requirements in this section." Those include SPF or DKIM authentication, valid forward and reverse DNS records, a TLS connection, and keeping "spam rates reported in Postmaster Tools below 0.3%."

Gmail, more than 5,000 a day. A second set applies to "email senders who send more than 5,000 messages per day to Gmail accounts." Those senders need SPF and DKIM, plus DMARC (Google notes "Your DMARC enforcement policy can be set to none"), a From: domain aligned with the SPF or DKIM domain, and one-click unsubscribe on marketing and subscribed messages with "a clearly visible unsubscribe link in the message body." For all senders, Google's guidance also says to keep spam rates "below 0.10%" and "avoid ever reaching a spam rate of 0.30% or higher."

Yahoo. Yahoo's requirements for all senders include SPF or DKIM and "Keep your spam rate below 0.3%." Its bulk sender requirements add SPF and DKIM together, a DMARC policy "with at least p=none," one-click unsubscribe, and "Honor unsubscribes within 2 days." Yahoo's best practices page doesn't put a number on what counts as bulk.

Those spam thresholds measure complaints, and a complaint is a different event from a bounce. Both get worse when you keep mailing addresses that were never good or people who stopped reading, so the same list cleaning helps both. Authentication links them too: Klaviyo's technical bounce category covers "missing DNS records or authentication problems."

What's a good email bounce rate?

We won't give you a number, because we couldn't find a published benchmark we'd stand behind. Klaviyo's bounce rate article explains the metric and how to lower it without setting a target. It does give you the formula: "The number of bounced emails divided by the total number of emails sent."

Watch your own trend instead, broken down by send, by signup source, and by inbox provider. A rise right after a new signup source or a list import tells you where the bad addresses came from.

Worked example (made-up numbers). A store sends a campaign to 40,000 profiles and 600 emails bounce. Bounce rate is 600 divided by 40,000, which is 1.5%. The bounce report shows 90 hard bounces and 510 soft bounces. The 90 hard bounces are already suppressed. Of the 510 soft bounces, 380 sit in one category at one inbox provider, which points to a sending problem with that provider rather than 380 bad addresses. The other 130 are spread out, and 45 of those profiles have at least 4 bounces in the last 90 days. Those 45 go into the chronic soft bounce segment.

How should you handle each bounce type in Klaviyo?

Here's the checklist we work through on an account.

Leave hard bounces suppressed. If you suspect a typo, Klaviyo suggests "correcting the email address and sending a one-off email. If the email still bounces, this address should remain suppressed." If you moved from Mailchimp, Klaviyo says bounced addresses synced from it are suppressed for bounces, so keep them that way. For other providers, Klaviyo says the suppression reason depends on the original suppression and how it's synced, so check it.

Pull chronic soft bouncers out early. Klaviyo recommends a segment of anyone "with at least 4 bounced emails in the last 90 days, and who can receive email marketing." It calls this "a recommended cleanup threshold, separate from the automatic suppression rule," and the 4 bounces don't need to be consecutive. Exclude that segment from campaigns, or suppress it.

Read bounces by category and provider. In Klaviyo, open Analytics, then Deliverability, then Email, then Bounce details. The heatmap covers "All 11 bounce categories, including External Error" and the inbox providers with the most bounced emails. One provider lighting up is a different problem from bounces spread across all of them.

Fix what the category points to. For technical bounces, Klaviyo's fix is to "Ensure you are passing SPF, DKIM, and DMARC." For frequency or volume, it says to reduce what you send to the affected provider and use batch sending. For reputation, it lists "Tighten sunsetting windows" and "Consider reducing your sending frequency." For message size, it recommends "an email size below 110KB."

Stop bad addresses at signup. Klaviyo strongly suggests keeping double opt-in on. It also flags giveaways and contests that sync into your main list as a way to pick up unengaged and fake emails.

Run a sunset flow. Klaviyo's fix for invalid address bounces includes a sunset flow "that will help reduce invalid address rejections by removing unengaged recipients before mailboxes become invalid." We cover how the sunset step works in our guide to winback flows, and where it sits among the Klaviyo flows every store needs.

Keep suppressed profiles instead of deleting them. Klaviyo says suppressed email profiles "do not count toward your email plan's active profile limit," and deleting profiles skews the segments you use for analysis. There's more on that in how Klaviyo works out your monthly bill.

When doesn't this apply?

A spike at one inbox provider. If one send bounces heavily at a single provider, look at your sending setup before you remove anyone. Klaviyo's advice for technical failures isolated to 1 mailbox provider is to check the detailed bounce reason and confirm your DNS records and authentication meet that provider's requirements.

Your own sender address is wrong. Klaviyo has a separate category, invalid sender address, for when "your sender email address is misspelled or does not exist." That's a settings fix, not a list problem.

SMS. Everything above is about email. Klaviyo's bounce rate article says it "specifically focuses on email bounce rates."

Open rate questions. Bounces measure delivery, not engagement. Google's guidelines say "Google doesn't track open rates" and that low open rates "aren't necessarily an accurate indicator of deliverability or spam classification issues." If opens are what worry you, read our guide to email open rate benchmarks first.

How does Hayes Media handle bounces for clients?

Hayes Media runs email, SMS, loyalty programs, and subscribe-and-save programs for eCommerce brands. We work in Klaviyo for most accounts and have experience in most other email and SMS platforms, so a brand on another platform is still a fit. Bounce data is part of the deliverability check in the email marketing audit we run before taking any client, next to authentication, spam complaint trends, and whether a sunset flow exists.

We typically work with brands doing at least $100K per month in revenue. It's a guideline, not a gate: a smaller brand with a clear budget set aside to scale and real order volume already qualifies. One-time email projects start from $2,000 USD, and retainers for ongoing full management start from $4,000 USD per month, scoped on the discovery call. You can see the full scope on our email and SMS service page, or read what an eCommerce email agency should do for you.

One honest limit: our case studies are published by us on our own site. We have no third-party review profile and no Klaviyo partner listing, so judge us on what the audit finds in your account.

Book a discovery call and we'll audit your bounce data, suppression rules, and sender authentication on your real account, then show you what to fix first. No onboarding fees. No lock-in contracts. No junior marketers.

Sources

Klaviyo help center, Understanding bounced emails in Klaviyo: https://help.klaviyo.com/hc/en-us/articles/115005250408

Klaviyo help center, Understanding suppressed email profiles: https://help.klaviyo.com/hc/en-us/articles/115005246108

Klaviyo help center, How to decrease bounce rates: https://help.klaviyo.com/hc/en-us/articles/360057036052

Google, Email sender guidelines: https://support.google.com/a/answer/81126

Yahoo Sender Hub, Sender requirements and recommendations: https://senders.yahooinc.com/best-practices/