Email deliverability is the ability to get accepted mail into the mailbox experience you intended, rather than having it rejected or filtered because of preventable technical or reputation problems. The highest-value work happens before a campaign is sent.
This page is the preventive checklist for the Proofy deliverability cluster. For troubleshooting after a problem appears, see why emails go to spam. For monitoring a reputation problem, see email sender reputation.
1. Authenticate Every Sending Domain
Set up SPF and DKIM correctly, publish DMARC, and verify alignment across every platform allowed to send on the domain. Gmail requires SPF or DKIM for all senders to personal Gmail accounts and SPF, DKIM, and DMARC for senders above its bulk-sender threshold.
For the implementation layer, see email authentication and DNS for deliverability.
2. Keep Spam Complaints Extremely Low
Google recommends keeping the user-reported spam rate below 0.1% and avoiding 0.3% or higher. Complaints usually indicate a mismatch between recipient expectations and sending behavior.
3. Make Unsubscribe Easy
Promotional mail should always provide a clear unsubscribe path. Gmail bulk senders must also support RFC 8058 one-click unsubscribe for marketing and subscribed messages. A frictionless opt-out is better than forcing an unhappy recipient to use the spam button.
4. Keep Contact Data Clean
Old, malformed, abandoned, and otherwise low-quality addresses create avoidable delivery failures. For broad database hygiene, use email list cleaning. For file-based verification, use bulk email verification.
5. Validate Addresses at Collection When It Matters
Signup forms, trials, account creation, and lead-capture workflows can use the Email Verification API to identify unusable or risky addresses before they move deeper into the stack.
6. Keep Sending Volume Predictable
Mailbox providers evaluate sending behavior over time. New or lightly used infrastructure should not jump abruptly from almost no mail to large campaign volume. Increase volume gradually and watch provider diagnostics as traffic scales.
7. Separate Different Mail Streams When Useful
Transactional, lifecycle, promotional, and re-engagement mail have different audience expectations and risk profiles. Separate subdomains or infrastructure can make monitoring and reputation isolation easier, especially at higher volume.
8. Monitor Provider-Specific Reputation
Use Google Postmaster Tools for Gmail-specific data such as spam rate, authentication, delivery errors, and available domain/IP reputation signals. Remember that each mailbox provider has its own view of the sender.
9. Suppress Permanent Failures and Respect Unsubscribes
Hard bounces and confirmed unsubscribes should not keep cycling back into future campaigns. Preserve suppression records across migrations and integrations.
For bounce-specific diagnostics, see why emails bounce and how to handle them.
10. Test the Actual Message Before a Major Send
Check links, HTML, sender identity, unsubscribe behavior, authentication, and rendering in the environments that matter. A pre-send test does not guarantee inbox placement, but it catches preventable mistakes before they reach the full audience.
Metrics to Watch
- User-reported spam rate: monitor provider-specific complaint data.
- Bounce categories: separate permanent failures from temporary ones.
- Authentication: watch SPF, DKIM, and DMARC pass/alignment results.
- Delivery errors: review rejection and deferral reasons by provider.
- Unsubscribe trends: spikes can reveal expectation or frequency problems.
What Deliverability Is Not
Deliverability is not one universal score, one open-rate target, one bounce-rate threshold, or one spam-word list. Google explicitly says it does not track open rates. Provider-specific reputation, complaints, authentication, sending behavior, and list quality are more useful operational signals.
Frequently Asked Questions
What should I fix first?
Start with authentication and recipient complaints. Then review sending behavior, list quality, suppressions, and message-level problems.
Does a clean list guarantee inbox placement?
No. List quality removes one source of risk, but authentication, complaints, infrastructure, and recipient expectations still matter.
Is the Gmail Promotions tab a deliverability failure?
No. Promotions is a Gmail inbox category, not the spam folder. The goal is legitimate delivery and recipient relevance, not forcing every marketing message into Primary.
Bottom Line
The strongest deliverability program is preventive: authenticate correctly, keep complaint rates low, maintain clean data, send predictably, honor unsubscribes, and monitor provider-specific diagnostics. Use this article as the hub, then move into the deeper technical, bounce, reputation, or spam-prevention guides when a specific problem needs investigation.
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