What does 'Resources restricted - exceeds recipients limit' bounce message mean and how to solve it?

Key findings

• Rate limiting: The message typically signifies that the recipient's mail server has a policy in place to limit the number of emails or recipients from a single sender's IP within a certain timeframe, often to prevent spam or manage server load.
• Soft bounce: A 451 bounce code is a soft bounce, meaning it's a temporary failure. The sending server will usually retry delivery later.
• Misleading message: In some cases, this specific bounce message can be misleading, triggered by an underlying issue like sending to a domain that doesn't actually exist (e.g., due to a typo in the domain name), leading to an unexpected bounce response rather than a clear 'recipient address rejected' or domain not found error.
• Domain-specific issue: While the bounce can appear across various recipient domains, it's often tied to specific domains that have stricter receiving policies or where an issue, such as a mistyped domain, is concentrated.

Key considerations

• Verify recipient domains: Before adjusting sending rates, confirm that the recipient domain is valid and correctly spelled. A simple DNS lookup (checking for MX records) can quickly reveal if the domain exists and accepts email.
• Adjust sending speed: If the domain is valid, consider slowing down your sending rate to the affected domain or ISP. Gradually increase it until you find an acceptable volume that doesn't trigger these limits.
• Monitor bounce reports: Pay close attention to your bounce logs for specific error codes and messages. This helps differentiate between genuine rate limits and other underlying problems that might masquerade as them, as discussed in our guide on troubleshooting rate limit exceeded messages.
• Recipient list hygiene: Regularly clean your email lists to remove invalid or inactive addresses. A clean list reduces bounce rates and improves overall deliverability, helping you avoid various email bounce scenarios.

Key opinions

• Initial interpretation: Many marketers initially interpret this bounce as a straightforward indication of sending too quickly to a specific domain or exceeding per-recipient limits, leading to an immediate thought of throttling.
• Unusual phrasing: The specific wording 'exceeds recipients limit' can sometimes be perceived as unusual, even if the underlying meaning points to rate limits, prompting marketers to seek clarification.
• Troubleshooting focus: The focus often shifts to verifying sending volumes against typical ISP limits or looking for other forms of rate limiting if the bounce is widespread on a particular domain.
• Impact of data errors: Misreporting or typos in domain names can lead to unexpected bounce messages, confusing the troubleshooting process and potentially masking the true problem.

Key considerations

• Verify recipient data accuracy: Always double-check the accuracy of recipient domains and email addresses, especially if a bounce message seems unusually worded or affects a high percentage of recipients for a specific domain.
• Proactive list cleaning: Regularly cleaning email lists is crucial to remove invalid or non-existent domains and addresses, preventing unnecessary bounces and maintaining a healthy sending reputation.
• Sender reputation: Consistent bounces, even soft ones, can negatively impact sender reputation, making it harder to reach the inbox. Address bounce issues promptly.
• Seek community insights: For obscure or confusing bounce messages, leveraging online communities and forums can provide valuable shared experiences and potential solutions, as highlighted by discussions on email bounce backs.

Key opinions

• Direct interpretation: Experts generally find the bounce message 'Resources restricted - exceeds recipients limit' to be quite self-explanatory, directly indicating that the sender is attempting to send too many emails or recipients too quickly for the receiving server's policy.
• MX record check: A crucial diagnostic step, according to experts, is to immediately check the MX (Mail Exchange) records of the problematic domain. A non-existent or misconfigured MX record can lead to unexpected and misleading bounce messages.
• Reporting accuracy: Experts warn against unquestioningly trusting bounce reports if initial checks (like domain validity) reveal discrepancies. Inaccurate reporting can mask the true cause of delivery failures and lead to incorrect troubleshooting.
• Aggressive throttling: For known problematic recipient domains, experts often advise significantly reducing sending rates and being extremely conservative with volume, even if it impacts delivery speed. This is sometimes the only way to get through.

Key considerations

• DNS diagnostics: Always perform DNS lookups, especially for MX records, when encountering unusual bounce messages. This fundamental step can quickly identify if the issue is with the recipient's domain itself, as highlighted in discussions around technical solutions for deliverability.
• Trust but verify: While bounce messages provide valuable feedback, experts emphasize verifying the information, particularly when the message seems to conflict with expectations or known domain status. If a domain `does not exist at all` it makes sense to trust that.
• Iterative rate adjustment: For actual rate limits, a methodical approach to reducing and then gradually increasing sending volumes can help find the optimal sending speed for difficult ISPs. This is a common strategy to prevent sender rejections.
• ISP-specific challenges: Some ISPs (like Optimum.net, previously optonline.net) are known to be particularly challenging for senders, requiring persistent adjustments and careful management of sending practices to ensure delivery. Referencing common ISP-specific deliverability advice can be helpful.

Key findings

• SMTP code interpretation: The SMTP `451` code signifies a temporary failure due to a transient condition. The `4.7.1` enhanced status code typically means a policy violation or general resource restriction, encompassing issues like exceeding recipient limits.
• Rate limiting policies: Documentation often details how receiving servers implement outbound and inbound email limits to protect against spam, manage server load, and ensure fair usage, which can lead to 'exceeds recipients limit' bounces.
• RFC compliance: Standard SMTP responses adhere to RFCs (Request for Comments) like RFC 5321 for mail transfer protocol. Understanding these standards helps in correctly interpreting bounce messages, even if they sometimes use slightly ambiguous phrasing.
• Distinguishing soft vs. hard bounces: Official guides clearly differentiate between temporary (soft) and permanent (hard) bounces. A 451 error is a soft bounce, prompting retries, whereas a 5xx error (e.g., 550 5.7.1 or 554) is permanent and requires list removal.

Key considerations

• Consult postmaster pages: For specific recipient domains, their postmaster pages or official documentation (e.g., Microsoft's Exchange Online limits) often provide detailed information about their sending policies, including recipient limits and throttling mechanisms.
• Adhere to best practices: Following general email sending best practices, such as maintaining good list hygiene and gradually warming up new IPs, helps mitigate the risk of hitting rate limits and reduces overall bounce rates, as detailed in various email deliverability guides.
• System resource issues: Some documentation, like Rackspace's common email bounces guide, may also link these errors to recipient server resource availability, suggesting temporary overload as a potential factor.