The short version
A bounce is a message the receiving system refused or could not deliver. Permanent failures should never be retried. Temporary ones should be, for a while. Your platform does the retrying and the suppressing for you, so your job is to read the bounce report for patterns: a typo-heavy signup form, an old imported list, or an authentication problem that makes one provider reject everything.
Bounces, especially hard ones, damage sender reputation, and MailerLite advises validating the rest of a list if a first send to it produces many hard bounces. [1] MailerLite also names a high number of bounces as one reason an account can be placed under review. [2]
SMTP code families in plain words
RFC 5321 sorts every server reply by its first digit. A 4yz reply means the command was not accepted but the error is temporary and the action may be requested again. A 5yz reply means the command was not accepted and the client should not repeat the exact request. [3] RFC 3463 adds enhanced codes in the form class.subject.detail, where 4.X.X is a persistent transient failure and 5.X.X a permanent one. [4]
The middle digit of the enhanced code tells you where to look: X.1 addressing, X.2 the recipient's mailbox, X.3 the receiving mail system, X.4 network and routing, X.5 protocol, X.6 content, X.7 security or policy. [4]
| Code | Meaning per the standard | Usually recorded as | What to do |
|---|---|---|---|
| 550 / 5.1.1 | Mailbox unavailable; bad destination mailbox address [3] [4] | Hard bounce | Check for a typo; otherwise let it stay suppressed |
| 552 / 5.2.2 | Exceeded storage allocation; mailbox full with a permanent class [3] [4] | Hard or soft, depending on platform | Leave it; ask the person for another address if they are a customer |
| 452 / 4.2.2 | Insufficient system storage; mailbox full as a transient failure [3] [4] | Soft bounce | Nothing; the platform retries |
| 450 | Mailbox unavailable, for example busy or temporarily blocked for policy reasons [3] | Soft bounce | If many share one domain, check authentication |
| 5.7.1 | Delivery not authorized, message refused [4] | Hard bounce | Check SPF, DKIM and DMARC before assuming bad addresses |
| 5.3.4 | Message too big for system [4] | Hard bounce | Reduce attachments and image weight |
| 4.4.7 | Delivery time expired [4] | Soft bounce that may convert | Look for a receiving domain that is down |
How each platform handles hard and soft bounces
Each row reflects what the vendor's own help or policy pages say. Plan billing for bounced contacts is only listed where the vendor states it.
| Platform | Hard bounce | Soft bounce | Soft to suppressed | Where to see it |
|---|---|---|---|---|
| MailerLite | Removed from the active list automatically; status becomes Bounced [5] | Stays in the active list [1] | Three soft bounces in a row count as a hard bounce [5] | Campaign report, Subscriber activity tab, bounce dropdown [1] |
| Kit | Status Bounced; unsubscribed and no longer emailed; not billed [6] | Stays Confirmed; Kit keeps trying future sends [6] | No threshold stated [6] | Subscribers, Status set to Bounced; profile Emails tab [6] |
| beehiiv | Permanently suppressed and dropped from future sends [7] [8] | Deferred mail retried for up to 72 hours, then counted as a block [8] | Can accumulate into a permanent suppression; no number stated [7] | Subscribers, Suppression list tab, with last bounce response [7] |
| Moosend | Not stated on its public pricing and features pages | Not stated on those pages | Not stated | Pricing page lists bounces, unsubscribes and complaints tracking [9] |
Working through a bounce report
Open the report after every send to a new or imported list, and monthly otherwise. In MailerLite it lives under Campaigns, Sent, View report, then the Subscriber activity tab, where a dropdown switches between hard and soft bounces. [1] In beehiiv, the Suppression list shows the type, date, reason and last bounce response for each address. [7]
- Sort by receiving domain. Many bounces at one domain point to a block or an authentication failure, not bad addresses.
- Look for typo domains such as gmial or hotmial. If the person is a real customer, contact them another way and ask them to sign up again through your double opt-in form.
- Read 5.7.x and policy text carefully. These are refusals, not dead mailboxes. Fix authentication first.
- Compare hard bounces by source. If one import or one form produces most of them, fix or retire that source.
- Leave soft bounces alone unless the same address keeps failing; the platform retries and converts or suppresses repeat failures.
- Export the bounced list and store it with your list records, so a future migration never re-imports those addresses.
- Do not re-add hard bounces manually. MailerLite's terms require removing addresses after three hard bounces. [10]
Worked example: a first send to an imported list
Assume you import 4,000 contacts collected over several years and send your first campaign. The report shows 140 hard bounces and 60 soft bounces.
Hard bounces are 140 of 4,000, or 3.5%. Most come from the oldest spreadsheet tab. That is the signal MailerLite describes: many hard bounces on a first campaign mean the rest of that source needs validating before the next send. [1] The 60 soft bounces need no action yet. If 20 of them share one company domain and show 450 or 5.7.1 text, that company's server is refusing you, which is an authentication or reputation problem rather than 20 dead mailboxes.
Next step: pause sends to the old source, validate it or drop it, and send the next campaign only to the recent, consented segment.
| Number | Calculation | Reading |
|---|---|---|
| Hard bounce rate | 140 / 4,000 | 3.5%: validate or drop the worst source |
| Soft bounce rate | 60 / 4,000 | 1.5%: let retries run |
| Delivered | 4,000 - 200 | 3,800 |
| Domain cluster | 20 of 60 soft bounces at one domain | Check SPF, DKIM, DMARC and that recipient's policy |
Bounces, complaints and your account
Bounces sit next to complaints in every platform's risk checks. MailerLite lists high bounces, spam complaints or unsubscribes, and sending to bought, scraped or unconsented addresses as reasons for account review, and says it may ask about list origin, consent and engagement history, with 30 days to respond. [2] beehiiv notes that many mailbox providers, including Gmail, do not send complaint feedback, so visible complaint rates can understate the real number. [8]
The practical rule is to prevent bounces at the source: confirmed signups, no old imports without cleaning, and authenticated sending.
Questions before you decide
Should I delete bounced subscribers?
You usually do not need to. Kit says bounced subscribers do not count toward your total or your bill. MailerLite removes hard bounces from the active list automatically. Keep the records so you never re-import those addresses on another platform.
When does a soft bounce become a hard bounce?
In MailerLite, after three soft bounces in a row. beehiiv says permanent suppressions can build up through repeated soft bounces but gives no number. Kit's help article gives no threshold and says soft-bouncing subscribers stay confirmed.
Why does a full mailbox sometimes come back as a permanent error?
RFC 3463 defines X.2.2 as mailbox full and says it should be used as a persistent transient failure, which is the 4.2.2 form. If a receiving server returns the permanent 5.2.2 form instead, a platform can record a full inbox as a hard bounce.
Can a hard-bounced address be reactivated?
Kit says its support team can remove the Bounced status where appropriate, for example after a technical problem or when the subscriber's address now works. beehiiv says permanent suppressions stay on the list because the addresses are undeliverable, and offers an appeal through support.
Sources & verification
Product details and prices can change. Check the linked provider before buying.
- MailerLite Help: The difference between a hard bounce and a soft bounce Accessed 30 Oct 2026
- MailerLite Help: Why is my account under review? Accessed 30 Oct 2026
- RFC 5321: Simple Mail Transfer Protocol Accessed 30 Oct 2026
- RFC 3463: Enhanced Mail System Status Codes Accessed 30 Oct 2026
- MailerLite Help: Subscriber statuses explained Accessed 30 Oct 2026
- Kit Help: Why is my subscriber showing as bounced? Accessed 30 Oct 2026
- beehiiv Support: Understanding your Suppression list Accessed 30 Oct 2026
- beehiiv Support: The email journey, key delivery events at beehiiv Accessed 30 Oct 2026
- Moosend: Pricing and trial FAQ Accessed 30 Oct 2026
- MailerLite: Terms of Use Accessed 30 Oct 2026
Sources link directly to providers. Product buttons may use separately labeled affiliate links. Read our disclosure.