Reference
Bounce categories
Hard and soft bounces grouped by cause, with typical SMTP codes, how Emailit classifies each one, its effect on suppressions and what to do about it.
A bounce is a message that couldn’t be delivered. This page groups bounces by cause so you can tell quickly whether to remove an address, fix your setup or simply wait. For individual codes, see SMTP reply codes and enhanced status codes.
Hard and soft bounces
| Hard bounce | Soft bounce | |
|---|---|---|
| Meaning | Permanent: the message will never be delivered as sent. | Temporary: the message might be delivered later. |
| Typical codes | 5xx replies, 5.x.x enhanced codes |
4xx replies, 4.x.x enhanced codes, timeouts |
| Emailit status | bounced |
attempted while Emailit retries |
| What Emailit does | Stops trying and may suppress the address. | Retries up to 7 times over about 21 hours, then bounces and suppresses the address. |
How Emailit classifies a bounce
Emailit classifies each failed delivery from the receiving server’s reply:
- Known permanent replies. Codes
550,551,553and554, and replies whose text says the failure is permanent, mark the emailbouncedright away. - Temporary replies treated as permanent. Common mailbox-full, over-quota, unknown-user, disabled-mailbox and relay-denied replies are treated as hard bounces even when they arrive with a
4xxcode, because retrying them rarely helps. - Everything else is retried. Other
4xxand5xxreplies, timeouts, connection errors and DNS failures mark the emailattempted. Emailit retries after 10, 20, 40, 80, 160, 320 and 640 minutes. After the seventh failed attempt the email isbouncedwith the reason “Maximum number of delivery attempts (7) has been reached.” - Asynchronous bounces. Some servers accept a message (
250, statusdelivered) and send a bounce message (DSN) to your return path later. Emailit matches the DSN to the original email and changes its status tobounced.
Some replies also slow delivery down for a while: a 451 pauses that IP-to-domain route for 5 minutes, and a 550 5.7.1 block that isn’t about content pauses it for 1 hour.
Effect on suppressions
If automatic suppression is on for bounces, Emailit adds the address to your suppression list in these cases:
| Situation | Suppressed |
|---|---|
| An asynchronous bounce (DSN) arrives for the email. | Immediately, with reason bounce. |
| The email fails all 7 delivery attempts. | Immediately, with reason too many soft fails. |
| A hard bounce, when the same address already hard bounced in the last 24 hours. | On the second hard bounce, with reason too many bounces. |
| The recipient reports the email as spam. | Immediately, as a complaint suppression (if complaints are suppressed). |
A successful delivery to an address removes its recipient suppression. Pay as you go workspaces always suppress bounces and complaints; on Pro and Business you can change this in WorkspaceSettings under Suppressions.
Categories
In the Suppression column, repeat means Emailit suppresses the address on its second hard bounce within 24 hours, and after retries means it suppresses the address when all 7 attempts fail. An asynchronous bounce suppresses the address right away in every category.
| Category | Type | Typical codes | Emailit | Suppression |
|---|---|---|---|---|
| Mailbox doesn’t exist | Hard | 550 5.1.1, 550 5.1.10, 553 5.1.3, 550 5.4.1 |
Bounced | Repeat |
| Domain doesn’t exist | Hard | 550 5.1.2, 5.4.4, no MX records |
Retried, then bounced | After retries |
| Mailbox full | Usually soft | 452 4.2.2, 552 5.2.2 |
Known over-quota replies bounced, others retried | Repeat, or after retries |
| Mailbox disabled | Hard | 550 5.2.1, Gmail 4.2.1 inactive |
Bounced | Repeat |
| Policy or blocked | Hard | 550 5.7.1, 554 5.7.1, 550 5.7.606 |
Bounced, with a 1-hour back-off for 550 5.7.1 |
Repeat |
| Spam or content | Hard | 550 5.7.1, 554 5.7.0 |
Bounced | Repeat |
| Reputation | Soft or hard | 421 4.7.0, 421 4.7.28, 550 5.7.1 |
4xx retried, 5xx bounced |
Repeat, or after retries |
| Rate limited or greylisted | Soft | 421, 450 4.7.1, 451 4.7.1 |
Retried, with a 5-minute back-off on 451 |
After retries |
| Message too large | Hard | 552 5.3.4, 552 5.2.3 |
Retried, then bounced | After retries |
| TLS required | Hard | 530 5.7.0 |
Retried, then bounced | After retries |
| Authentication failure (DMARC) | Hard | 550 5.7.26, 550 5.7.509, 550 5.7.515, 550 5.7.23 |
Bounced | Repeat |
Mailbox doesn’t exist
The address was never created, was deleted, or has a typo. Example: 550 5.1.1 The email account that you tried to reach does not exist.
What to do: Remove the address from your lists. If many addresses from one source bounce this way, the source is the problem, so verify the list before you send to it again.
Domain doesn’t exist
The recipient’s domain has no MX or A record, often because of a typo such as gmial.com or an expired domain. Because DNS failures can be temporary, Emailit retries before it bounces the email.
What to do: Fix the typo or remove the address. Validate addresses at sign-up so typos don’t reach your list.
Mailbox full
The recipient is over their storage quota. Example: 452 4.2.2 The email account that you tried to reach is over quota. Emailit treats the common over-quota replies as hard bounces so it doesn’t keep retrying a mailbox that’s unlikely to be emptied.
What to do: Nothing for one-off cases. An address that stays full is usually abandoned, so remove it.
Mailbox disabled
The account exists but was closed, suspended or marked inactive by the provider. Example: 550 5.2.1 The email account that you tried to reach is disabled.
What to do: Remove the address.
Policy or blocked
The receiving server refused the message because of a local policy: a blocklist, a firewall rule, or a recipient that only accepts mail from known senders. The address itself may be fine. Example: 550 5.7.1 Service unavailable, client host blocked using Spamhaus.
What to do: Read the message text for the reason and any link. If it names a blocklist, check your recent complaint and bounce rates, then contact support with the full reply. See best practices.
Spam or content
A spam filter rejected the message because of its content, links or attachments. Example: 554 5.7.1 Message rejected as spam.
What to do: Check the email’s Spam Checks panel, remove URL shorteners and links to domains with a poor reputation, balance images with text and send a plain-text part. Emailit also holds messages that score 7 or more before they’re sent. See Spam checks.
Reputation
The provider distrusts your sending domain or IP because of past complaints, bounces or spam-trap hits. Gmail, for example, defers with 421 4.7.28 when it sees an unusual rate of unsolicited mail.
What to do: Lower volume to that provider, stop sending to unengaged and unverified addresses, and watch your sending health. Warm up new domains gradually. See Warm-up.
Rate limited or greylisted
The receiving server is throttling you or wants an unfamiliar sender to try again later. Example: 451 4.7.1 Greylisting in action, please come back later.
What to do: Nothing. Emailit’s retries handle greylisting and short throttling. If one provider defers most of your mail for hours, send in smaller batches.
Message too large
The message is over the receiving server’s size limit, which is often 25 MB or less even though Emailit accepts up to 40 MB. Encoding attachments adds about a third to their size.
What to do: Send smaller attachments or link to the files instead. See Attachments.
TLS required
The receiving server only accepts encrypted connections. Emailit’s MTA upgrades to TLS whenever the receiving server offers STARTTLS, so this bounce is rare and usually points to a misconfigured receiving server.
What to do: Contact support with the full reply.
Authentication failure (DMARC)
The message failed SPF and DKIM alignment and the From domain’s DMARC policy is quarantine or reject, or the provider requires authentication from all senders. Examples: 550 5.7.26 Unauthenticated email from acme.com is not accepted due to domain's DMARC policy. and 550 5.7.509 Access denied, sending domain acme.com does not pass DMARC verification.
What to do: Check that the sending domain is verified in Emailit, so DKIM signs with your domain. If another service sends as your domain, fix its SPF and DKIM too, and use DMARC reports to find it.
Complaints aren’t bounces
A spam complaint means the email was delivered and the recipient marked it as spam. Emailit receives complaints through feedback loops, sets the status to complained, sends an email.complained event and suppresses the address as a complaint. Treat complaints more seriously than bounces: they hurt your reputation faster.