Email deliverability is how reliably your emails reach the inbox instead of bouncing or landing in spam. It depends on authentication (SPF, DKIM, DMARC), sender reputation, list quality and engagement. Bounce rate, the percentage of emails that couldn't be delivered, is one of its most important warning signals.
Hard vs soft bounces
- Hard bounce: permanent failure, such as an address that doesn't exist. Remove it immediately.
- Soft bounce: temporary failure, such as a full mailbox or a server issue. Retry, then remove if it keeps failing.
High bounce rates tell mailbox providers your list is poorly maintained, which hurts reputation.
What improves deliverability
- Authenticate your domain (SPF, DKIM, DMARC)
- Validate lists before sending
- Send to engaged, opted-in contacts
- Keep spam complaints very low (Google's guidance: never reach 0.3%)
- Warm up new domains and keep volumes steady
Example
After importing an old trade-show list, a company sees bounces spike and opens drop. It validates the list, removes invalid addresses, and sends only to recent engagers for two weeks. Inbox placement recovers.
Related terms
SPF · DKIM · DMARC · List hygiene · Open rate
Guide: email deliverability in 2026.
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