Delivery Rate Thresholds and Domain Blocking

Mailbox providers measure two ratios for every sending domain: the share of messages that bounce, and the share marked as spam. Both are tracked per sending domain and per IP address. Once either ratio crosses a threshold, the resulting restriction applies to the domain as a whole, not only to the campaign that caused it.

Acceptable delivery rate

Providers do not publish exact cutoffs. The following ranges reflect industry consensus, based on the public bulk-sender guidelines of Gmail and Yahoo.

• A bounce rate below 2% is considered healthy. A rate between 2% and 5% affects inbox placement. A rate above 5% indicates a poorly maintained list.
• A complaint rate below 0.1% is recommended. Gmail and Yahoo require it to stay below 0.3%.
• Both ratios are measured over a rolling period, not a single send. One campaign can lower the average for several days.

Domain-wide blocking after a threshold breach

Mailbox providers assign sender reputation at the domain and IP level, not per campaign. Once the bounce or complaint rate crosses the threshold, the restriction applies to every message sent from that domain, including transactional mail such as password resets or receipts.

• Throttling. The provider slows acceptance or delays delivery instead of an outright rejection.
• Spam-folder placement. Messages are accepted but not delivered to the inbox.
• Full blocking. The domain or sending IP is placed on a blocklist, such as Spamhaus or SORBS, or on the provider's internal list. Delivery stops until the reputation recovers, a process that can take several weeks.

The restriction applies to the entire domain. A single low-quality import, such as a purchased list, an outdated export, or an unvalidated signup form, can reduce deliverability for all mail sent from that domain.

Reducing bounce rate with CleanContact

The bounce component of the ratio is addressed by address validation performed before a message is sent.

• Validation at the point of capture prevents a dead or mistyped address from entering the list.
• Re-validation of existing lists before a large send accounts for addresses that become inactive over time.
• Handling of disposable domains and catch-all configurations identifies addresses that a standard SMTP check would classify as valid.

Fewer hard bounces per campaign keep the domain within the 2% range used by providers as an acceptance threshold.

Sources of delivery rate data

Bounce rate is available in standard sending reports. Complaint rate is not. This figure is obtained from feedback loops (FBL) and related reporting mechanisms such as DMARC, made available to sender domains after registration or verification of ownership.

Gmail - Postmaster Tools

Google does not operate a third-party feedback loop. Postmaster Tools provides the equivalent function: a dashboard showing the domain's spam rate, IP and domain reputation, and delivery errors as observed by Gmail.

• Add the sending domain at postmaster.google.com.
• Verify ownership with a TXT record in DNS, using the same method as domain verification in Search Console.
• Data becomes available once sufficient volume is sent through Gmail. Review the Spam Rate chart during a campaign.

Yandex - DMARC reports

Yandex discontinued its Postmaster dashboard in September 2020 and has not introduced a replacement. Delivery and complaint data for Yandex is obtained through DMARC aggregate reports, which any DMARC-compliant receiver, including Yandex, sends to the domain owner regardless of whether a dashboard exists.

• Publish a DMARC record for the domain with a rua= tag pointing to an address or service that collects reports.
• Aggregate reports are delivered approximately once per day in XML format. Each report includes delivery and authentication results by provider, including Yandex.
• A DMARC monitoring service, such as dmarcian or Postmark's DMARC Digests, converts these reports into a readable format.

Mail.ru - Postmaster

postmaster.mail.ru provides reputation, delivery, and feedback-loop registration for Mail.ru sender domains.

• Register at postmaster.mail.ru and confirm domain ownership with a DNS TXT record.
• Enable the feedback loop in account settings to receive complaint notifications for individual messages.
• Review the reputation dashboard before and after large sends to identify a rate increase at an early stage.

Monitoring the Gmail and Mail.ru dashboards, together with DMARC reports for Yandex, provides ongoing visibility into deliverability rather than relying on the disappearance of a campaign as the first indication of a problem.