Deliverability
Email deliverability, sender reputation and diagnosis
Understand email delivery, sender reputation and how to investigate authentication, bounces and recipient response in an Australian email programme.
Email deliverability is whether a message reaches a place where its recipient can use it, such as the inbox. A platform’s “delivered” count usually means it recorded no bounce; it does not prove inbox placement.
Sender reputation is a receiving service’s assessment of mail associated with a domain or IP address. Providers use proprietary scoring systems and signals that include bounce rates, spam complaints, recipient engagement, authentication and sending consistency.
List quality and spam-trap hits can also affect reputation, while sudden changes in sending volume may trigger scrutiny. A dedicated IP builds its own history; a shared-IP environment distributes risk across senders.
When results worsen, distinguish a sending or rejection problem from accepted mail that may have been filtered, and from a campaign whose recipients chose not to act. That distinction helps direct the investigation.
Separate the signals
| Signal | What to check | Limit |
|---|---|---|
| Sent | How many messages the platform attempted | An attempt does not establish acceptance. |
| Accepted or reported as delivered | Receiver replies, bounces and the platform’s counting rule | Acceptance does not establish inbox placement. |
| Recipient action | Recorded clicks or a reliably attributed later action | Silence does not identify its cause. |
Keep counts beside rates. A lower click rate may reflect the audience, message or destination, while a low bounce rate does not prove strong inbox placement.
Three levels of delivery evidence
- SentMessages the platform attempted. An attempt does not establish acceptance.
- Accepted or reported as deliveredReceiver replies, bounces and the platform’s counting rule. Acceptance does not establish inbox placement.
- Recipient actionRecorded clicks or a reliably attributed later action. Silence does not identify its cause.
Check the sending identity
List the services that send using your visible From domain, including campaign and automated systems. Check the identity each route uses and the authentication results on a received message from that route.
SPF authorises sending hosts, DKIM associates a signing domain with a message through a cryptographic signature, and DMARC lets a domain owner publish policies for validation and handling. Authentication helps establish identity but cannot guarantee inbox placement.
Confirm a route’s setup with its sending provider before changing DNS. Check provider guidance for detailed SPF, DKIM and DMARC configuration.
Check receiver-specific requirements
Since 1 February 2024, all senders to personal Gmail accounts must use SPF or DKIM, have valid forward and reverse DNS records, transmit over TLS, format messages to RFC 5322, keep the spam rate reported in Postmaster Tools below 0.3%, and not impersonate Gmail From headers.
Senders sending more than 5,000 messages per day to Gmail accounts must also use both SPF and DKIM and set up DMARC; the DMARC policy can be set to none. Google also requires these senders to keep the reported spam rate below 0.30%, and these requirements are specific to Gmail.
Gmail sender requirements at a glance
- 1Requirements effective from
- 5,000Stricter rules apply above
- 0.30%Reported spam rate ceiling
Check permission and recipient expectations
Permission means recipients have agreed to receive the kind of email you send and understand what to expect. Unexpected or out-of-context messages can lead to complaints and unsubscribes.
The message should match what recipients were told to expect. Review complaints and unsubscribes alongside delivery results; a DNS change cannot resolve an audience or content mismatch.
For Australian guidance, consult ACMA’s “Avoid sending spam” guidance when reviewing permission and recipient expectations.
Follow the stage that changed
If bounces rise, compare failures by recipient domain and sending route, and retain the receiver replies. Those replies provide more diagnostic detail than a platform’s broad “hard” or “soft” label.
If messages are accepted but response falls, compare similar audiences and messages before treating reputation as the cause. Review the offer and destination, then use relevant receiver-side data where available.
Record when the change began, who was affected, the diagnostic replies and any setup changes. Repair confirmed sending faults before retrying, suppress confirmed invalid addresses, and keep unsubscribed contacts excluded.
Judge a correction against the next appropriate send and its recipient mix, rather than one dashboard number. Open counts need care because Apple Mail Privacy Protection can affect opens and open-related metrics; use a reliably measured downstream action where it fits the campaign’s purpose.
Diagnosing a change in results
- Identify which stage changedDistinguish a sending or rejection problem from accepted mail that may have been filtered, and from recipients simply not acting.
- If bounces riseCompare failures by recipient domain and sending route, and keep the receiver replies — they carry more detail than a platform’s broad “hard” or “soft” label.
- If mail is accepted but response fallsCompare similar audiences and messages before treating reputation as the cause. Review the offer and destination, then check relevant receiver-side data.
- Record the changeNote when it began, who was affected, the diagnostic replies and any setup changes.
- Repair before retryingFix confirmed sending faults, suppress confirmed invalid addresses, and keep unsubscribed contacts excluded.
- Judge the correctionAssess the next appropriate send against its recipient mix, not a single dashboard number.
Use receiver data as a diagnostic aid
Google Postmaster Tools reports signals for outgoing email to personal Gmail accounts. Its dashboards cover compliance status, spam rate, IP and domain reputation, feedback loop, authentication, encryption and delivery errors.
The IP and domain reputation dashboards show quality ratings. The spam-rate dashboard shows the percentage of messages recipients manually mark as spam, the feedback-loop dashboard shows campaign messages marked as spam, and the authentication dashboard shows the percentage passing SPF, DKIM and DMARC.
Select a verified domain and a consistent time range to compare changes. Available ranges are the last 7, 30, 60, 90 or 120 days, and dashboard times use Coordinated Universal Time (UTC).
Dashboard data is not real-time: changes are typically reflected within 24 hours, but can take longer. Some dashboards show data only for DKIM-authenticated messages, and data may be missing on low-volume days.
Postmaster Tools attempts to exclude forwarded messages, but some dashboards may include them. Treat its data as a Gmail-specific view, and use available receiver-side signals for recipients on providers such as Microsoft 365 and Yahoo as well.
Google Postmaster Tools dashboards
- Compliance status
- Spam rate (percentage of messages recipients manually mark as spam)
- IP and domain reputation quality ratings
- Feedback loop (campaign messages marked as spam)
- Authentication (percentage passing SPF, DKIM and DMARC)
- Encryption
- Delivery errors
In this guide
- What SPF, DKIM and DMARC each doLearn what SPF, DKIM and DMARC check, how alignment works and why authentication does not guarantee inbox placement.
- Investigating a sudden rise in bounced emailsInvestigate a sudden bounce spike using SMTP replies, recipient groups, sending routes and a controlled follow-up.
- Separating domain reputation from campaign engagementCompare domain-level delivery signals with campaign actions without drawing conclusions from a single reputation, spam or open-rate figure.
