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Manage Sending IP Reputation and Handle TSS04 Deferrals

This article explains practical steps customers can take to manage and optimize email sending IPs for better deliverability and reputation, and explains how Paubox handles IP reputation and mitigation for temporary recipient-side blocks.

Summary

  • Paubox actively monitors and manages outbound IP reputation and handles IP-level mitigation and routing at the infrastructure level.
  • Recipient providers (for example, AOL/Yahoo) may temporarily defer mail from an IP with a 421 4.7.0 [TSS04] error when they detect unexpected volume or user complaints. The guidance below covers actions you can take and how Paubox will respond.

How Paubox manages sending IPs

  • IP assignment and outbound routing are controlled by Paubox infrastructure and are not configurable on a per-customer or per-message basis.
  • Paubox monitors IP reputation continuously and performs mitigation and routing changes at the infrastructure level to protect delivery and reputation.
  • If recipient domains temporarily block an IP (e.g., 421 4.7.0 [TSS04]), Paubox can escalate to technical operations for investigation when customers report ongoing or critical delivery issues.
  • For real-time information about widespread issues, check the system status page.

Common recipient-side IP deferral (421 4.7.0 [TSS04])

  • Meaning: The 421 4.7.0 [TSS04] deferral indicates that providers such as AOL/Yahoo are temporarily deferring messages from the sending IP because of unexpected sending volume or user complaints. This is an IP reputation-related action taken by the recipient provider.

Customer actions to improve deliverability and reduce IP reputation risk

  1. Configure sender authentication

    • Ensure your domain has correct SPF and DKIM DNS records. These industry-standard records validate your messages and help prevent them from being flagged as spam.

  2. Preserve domain reputation

    • Avoid sending mass mailings from transactional or sensitive-address domains.
    • Do not use purchased lists. Sending to lists with unknown or unengaged recipients increases complaints and negative signals.

  3. Follow content best practices

    • Avoid including attachments or links that commonly trigger spam filters in routine or marketing messages.
    • Double-check recipient addresses for typos before sending.
    • Keep outreach content relevant and expected by recipients to lower complaint rates.

  4. Recipient-side remediation steps

    • Ask key recipients to check spam folders and mark your messages as “not spam.”
    • Request that recipients add your sending address or domain to their safe senders / whitelist lists.

  5. Retry strategy for temporary deferrals

    • Wait and retry sending later; recipient-side deferrals like TSS04 are often temporary.
    • Avoid multiple rapid retries in a short period, as repeated attempts can worsen reputation signals.

When to contact Paubox support

  • If delivery problems persist across multiple recipients or domains, provide details (impacted domains or recipients and timing) so Paubox can investigate IP reputation and escalate to technical operations.
  • For urgent delivery needs, Paubox can escalate at the infrastructure level to pursue mitigation with recipient providers.

Operational reminders

  • Paubox handles IP-level routing changes and mitigation internally; customers cannot request a one-time alternate outbound IP for a single message.
  • Use the system status page to monitor known or widespread infrastructure issues that could affect delivery.

Conclusion Maintaining strong deliverability and IP reputation requires both provider-level management and sender best practices. Keep SPF and DKIM correct, avoid risky mailing practices (purchased lists, unexpected mass sends), follow content best practices, ask recipients to whitelist where appropriate, and use measured retry behavior after temporary deferrals. Paubox continuously monitors and manages sending IP reputation and will investigate or escalate persistent issues when provided with recipient/domain details.