Understanding bounces
Hard versus soft bounces, the codes behind them, what SendCanyon does automatically, and when a bounce spike means stop.
A bounce is a message the receiving server refused or returned. Bounces are inevitable in small numbers — people change jobs, mailboxes fill up — but their *rate* is one of the two metrics (with spam complaints) that receiving providers watch most closely. Understanding the difference between bounce types tells you whether a number is noise or an emergency.
Hard bounces: permanent failures
A hard bounce (SMTP 5xx codes like 550 5.1.1 user unknown) means the address is permanently undeliverable: the mailbox doesn't exist, the domain is dead, or the server rejects the sender outright. SendCanyon reacts automatically: the contact's status flips to bounced, the address is added to your suppression list, and all remaining sequence steps for that contact are cancelled. A hard-bounced address is never retried.
Soft bounces: temporary failures
A soft bounce (4xx codes) is a temporary condition: mailbox full, server briefly unavailable, message greylisted pending a retry, or the sender being rate-limited. SendCanyon retries soft bounces with backoff over roughly 48 hours; if every retry fails, the failure is recorded, and an address that soft-bounces persistently across multiple campaigns gets escalated to bounced status.
| Signal | Likely cause | What to do |
|---|---|---|
| Isolated soft bounces | Full mailboxes, transient errors | Nothing — retries handle it |
| Cluster on one receiving domain | That company greylists or rate-limits you | Let retries spread the sends; don't re-blast |
| Cluster from one of your mailboxes | That mailbox is being provisionally distrusted | Drop its volume, check warmup floor, watch for a week |
| Soft bounces rising across all mailboxes on a domain | Domain reputation slipping — early spiral | Cut volume in half, verify DNS still passes, re-warm |
Reputation blocks dressed as bounces
Some 5xx responses aren't about the recipient at all — codes like 550 5.7.1 blocked or wording that references sender reputation, blocklists, or policy mean the receiver is rejecting you. These are the bounces to take most seriously: they show up in the bounce breakdown flagged as policy blocks. One or two from a small receiver is noise; policy blocks from Gmail or Microsoft mean stop sending and diagnose (DNS records, recent bounce spikes, complaint events) before the block hardens.
Where to see bounce data
- Analytics → Deliverability — bounce rate over time, split by campaign, mailbox, and domain, with hard/soft/policy breakdown.
- Campaign detail → Activity — the individual bounce events with the raw SMTP response per message.
- Webhooks — subscribe to
email.bouncedto mirror bounce events into your own systems in real time.
The compressed rulebook: hard bounces are a list-quality problem you fix before sending (validate every import); soft bounces are a pacing problem the system handles; policy blocks are a reputation problem you stop for. If bounce rate trips the 2% wire, the fix is never "finish the campaign first."