If your password resets, receipts, or onboarding emails are landing in spam or arriving late, you are usually dealing with domain reputation. It is the trust mailbox providers build around your sending domain based on authentication, user feedback, and sending patterns.
This matters most for SaaS and development teams sending transactional email because failures look like product reliability issues. A missing OTP is not a marketing problem, it is an incident. The good news is that domain reputation is not magic. You can improve it by making your sending identity clear, keeping bounces and complaints low, warming up new domains gradually, and using logs and events to stop repeated bad sends.
This guide gives a step-by-step checklist, common mistakes teams make while scaling, and a troubleshooting playbook for sudden drops. It focuses on the signals you can control and how to monitor them.
MailCub Documentation is helpful for verifying authentication setup and delivery visibility, and the Transactional Email Service page is relevant for event and webhook-based tracking. You can also review MailCub Pricing when planning sending scale and growth.
MailCub Documentation is a good starting point to verify SPF and DKIM early so you can reduce avoidable deliverability issues before they grow.
Quick Answer
- Set up SPF, DKIM, and DMARC so receivers can authenticate your email and reduce spoofing risk.
- Keep spam and complaint rates very low and investigate spikes quickly.
- Suppress hard bounces fast and do not keep retrying invalid recipients.
- Warm up new domains gradually instead of sending high volume on day one.
- Use logs and events to see which provider rejected mail and why, then automate suppression and smarter retries.
Why It Matters
Inbox placement affects activation, retention, and support load. When critical emails go to spam, users think your product is broken. When delivery is throttled, OTPs and magic links become slow and sign-in flows fail.
Reputation issues are also expensive to debug without visibility. The fastest teams treat deliverability like observability: they track statuses, failure reasons, and trends by mailbox provider, then change behavior based on real data instead of guessing.
Domain Reputation: Key Signals That Drive Inbox Placement
Mailbox providers evaluate trust using identity signals, feedback signals, and behavior signals.
Identity (who are you?): SPF and DKIM help prove you are authorized to send. DMARC adds policy and reporting, which helps reduce spoofing and improve trust.
Feedback (do users want this?): Spam complaints are a strong negative signal. The source content notes that for Gmail, Google recommends keeping spam rate under 0.1% and avoiding 0.3% or higher.
Quality and behavior (are you sending responsibly?): High hard bounce rates, sudden volume spikes, inconsistent From or signing domains, and repeated retries to bad addresses can all hurt reputation.
| Signal | What to monitor | What “good” looks like | First fix when it’s bad |
|---|---|---|---|
| SPF/DKIM/DMARC | Auth pass + alignment | Consistent pass/aligned identity | Fix DNS + align From/signing |
| Spam/complaint rate | Spam feedback rate | Very low; avoid 0.3%+ | Reduce unexpected mail + tighten triggers |
| Hard bounces | Invalid mailbox failures | Low; suppressed quickly | Validate signups + suppression list |
| Deferrals/throttling | Deferred/429-ish patterns | Rare, stable pattern | Slow ramp + backoff retries |
| Blocks/listings | “blocked” errors | None | Pause + remediate root cause |
| Consistency | Domain changes + spikes | Predictable volume | Warm-up + steady sends |
Step-by-Step Solution
1) Use a stable transactional sending domain
Pick a dedicated subdomain like notify.yourdomain.com for product and transactional mail. This keeps signals cleaner and reduces cross-impact from marketing experiments.
Keep the From domain consistent across password resets, OTPs, and alerts. Consistency matters more than clever naming.
2) Implement SPF, DKIM, and DMARC correctly
Publish SPF and DKIM for your sending domain first, then add DMARC. Start DMARC in monitoring mode and move toward stronger enforcement when your setup is stable.
Do not rotate signing domains during warm-up. You want a clear history tied to one identity.
MailCub Documentation is the right reference to verify your sending domain and DNS records for transactional email setup.
3) Stop hard bounces from repeating
Hard bounces are not transient. Suppress them immediately and avoid repeated sends to invalid recipients. The source content also notes AWS SES guidance recommends not making repeated attempts after a hard bounce.
If hard bounces start rising, investigate the source quickly. Common causes include typos, bots, imported bad lists, or broken signup validation.
4) Reduce spam complaints by making mail expected
For transactional streams, users expect urgent and useful messages, not surprise promotions. Keep transactional emails purely transactional and avoid adding marketing content into security or account flows.
If complaints rise, reduce frequency, tighten triggers, and pause borderline notifications until rates stabilize. The source content references Google’s spam-rate guidance as a useful benchmark.
5) Warm up new domains gradually
New domains have no reputation history. Do not send large volume on day one. Start with small daily volumes to your cleanest and most engaged recipients, then ramp steadily while watching complaints, bounces, and deferrals.
If you must send critical email immediately, keep volume modest and focus first on clean recipients and correct authentication.
6) Monitor reputation signals with the right tools and the right domain
The source content notes Gmail Postmaster Tools reporting is tied to the authenticated domain used for DKIM (or SPF fallback). If your authenticated domain differs from your visible From domain, the reputation view can look confusing.
Monitor outcomes by provider on your side as well: delivered, deferred, bounced, blocked, and failure reasons over time.
MailCub Documentation describes Email Logs with delivery statuses and error information, which is exactly what teams need for operational debugging.
MailCub Documentation is also useful for setting up email logs and delivery events so your team can trace bounce and deferral patterns without guesswork.
7) Use webhooks and events to automate suppression and smarter retries
Event-driven handling closes the loop:
- Hard bounce → suppress recipient
- Complaint → suppress recipient
- Deferred → retry with backoff
- Blocked → pause and investigate
The Transactional Email Service page highlights real-time tracking and webhook or event support, which fits this workflow well and helps prevent repeated failures.
Common Mistakes
- Sending from a new domain at full volume without warm-up.
- Missing or misaligned SPF, DKIM, or DMARC records.
- Retrying permanent failures repeatedly instead of suppressing them.
- Mixing marketing content into transactional flows, which increases complaint risk.
- No provider-specific visibility, so you cannot tell whether Gmail or Outlook is the issue.
- Changing From or signing domains too often and resetting reputation history.
Domain Reputation Troubleshooting
When inbox placement drops, diagnose by symptom and timeframe instead of changing everything at once.
If Gmail placement dropped this week
Check Postmaster Tools for the authenticated domain you actually use (DKIM or SPF domain). If you recently changed signing domains, your trend line may be showing a different domain than you expected.
Then compare the same time window to complaint and bounce spikes. If spam rate increased, reduce non-essential sends and tighten triggers first.
If deferrals or throttling increased
This often happens after volume spikes or reputation pressure. Slow the ramp and implement retry backoff instead of aggressive resends.
If messages are blocked
Pause high-volume sending, inspect the rejection reason, confirm authentication alignment, and check for listings. Do not try to push through a block with more volume.
MailCub Documentation and the Transactional Email Service together provide the most relevant references here for log visibility, delivery status, and webhook-based outcomes.
FAQ
What is domain reputation in email?
Domain reputation is mailbox-provider trust in your sending domain based on authentication, user feedback such as complaints, bounces, and overall sending behavior.
How long does it take to build domain reputation?
Usually days to weeks depending on volume and recipient quality. A steady warm-up ramp is safer than sudden spikes.
Do SPF, DKIM, and DMARC guarantee inbox placement?
No. They improve authentication and reduce spoofing risk, but mailbox providers still decide inbox or spam placement using many signals.
What spam or complaint rate should I aim for?
Keep it very low. The source content notes Google recommends staying under 0.1% and avoiding 0.3% or higher.
What should I do with hard bounces?
Suppress them immediately and do not keep sending to invalid addresses. Repeated attempts can damage reputation.
Why does Postmaster Tools show reputation for a different domain than my From address?
Because reporting is tied to the domain used for DKIM authentication (or SPF fallback), not always the visible From domain.
Conclusion
Domain reputation improves when your sending identity is clear, negative feedback stays low, and sending patterns remain predictable. If you also add logs and event-based suppression, you can stop repeat failures that quietly damage inbox placement over time.
Use MailCub Documentation to verify SPF and DKIM, review email logs, and implement delivery events. Pair that with the Transactional Email Service for transactional sending workflows, and review MailCub Pricing when you are ready to compare plans and scale sending volume.