What does 'Resources restricted - exceeds recipients limit' actually mean?

This bounce indicates that the recipient's mail server has temporarily blocked your email because you've exceeded its limits on how many emails or recipients you can send to within a certain timeframe. It is often a soft bounce, meaning the server might accept the email later if you reduce your sending rate. This differs from a hard bounce, which means permanent rejection.

What are the common reasons for this bounce?

The primary causes are sending too many emails to a single domain too quickly, or having a high number of invalid or inactive addresses in your list. A low sender reputation can also cause recipient servers to enforce stricter limits more readily. Check your bounce logs for patterns and specific problematic domains.

How can I resolve this bounce error?

Begin by analyzing your bounce logs to identify problematic domains. Implement email throttling to reduce your sending speed to affected domains. Crucially, clean your email list by removing invalid or unengaged addresses to improve overall list hygiene.

Does sender reputation play a role in this type of bounce?

Yes, maintaining a strong sender reputation is vital. This includes ensuring proper email authentication (SPF, DKIM, DMARC) and consistent sending behavior. A good reputation signals trustworthiness to receiving servers, making them less likely to impose strict limits on your mail.

Is this a hard bounce or a soft bounce, and what is the difference?

Unlike a hard bounce, which is a permanent failure (e.g., recipient address does not exist), a soft bounce like this indicates a temporary issue. The receiving server is asking you to pause or slow down rather than rejecting the email permanently. While a soft bounce may eventually go through, repeated soft bounces can negatively impact your sender reputation and lead to more permanent blockages.

What does 'Resources restricted - exceeds recipients limit' bounce message mean and how to solve it? - Troubleshooting - Email deliverability - Knowledge base

Receiving a bounce message that reads "Resources restricted - exceeds recipients limit" can be frustrating, especially when you are trying to ensure your emails reach their intended inboxes. This message typically indicates a temporary blockage by the recipient's mail server, signaling that your sending volume or rate to that specific domain (or even a specific recipient) has exceeded its predefined limits.

It is classified as a soft bounce, meaning the mail server acknowledges the email but cannot deliver it at that moment. Unlike a hard bounce, which indicates a permanent problem with the recipient address, a soft bounce suggests a temporary issue that might resolve itself or requires adjustments to your sending practices. Understanding this bounce is key to maintaining good email deliverability.

Understanding the 'resources restricted' bounce message

When you encounter the "Resources restricted - exceeds recipients limit" bounce message, the underlying cause is almost always related to how the recipient server perceives your sending behavior. Mail servers have internal mechanisms to protect their infrastructure and users from excessive mail, which includes implementing recipient limits and rate limiting. These limits can be per hour, per day, or per connection.

The 451 4.7.1 SMTP code often accompanies this bounce, indicating a temporary failure due to resource limitations. This differs from other common bounce errors such as "access denied" or messages related to rate limits exceeding, which might point to different underlying issues. For instance, Microsoft sometimes uses this message when your tenant exceeds its daily limit for sending to external recipients, which highlights an account-level restriction.

Even if your email content is legitimate and your sending practices generally follow best practices, a sudden spike in volume to a particular domain can trigger this response. It is the recipient server's way of saying, "Slow down, you're sending too much too quickly." Ignoring these warnings can lead to more severe deliverability problems, including being placed on a blacklist (or blocklist).

Common causes of recipient limits being exceeded

Several factors can contribute to hitting a recipient limit, even with moderate sending volumes. One common reason is simply sending too many emails to a single domain within a short period. Each mail server has its own internal thresholds, and exceeding them will result in this bounce. This is often an automated defense mechanism against potential spam or abuse, designed to protect the integrity of the recipient’s service.

Another significant factor is poor list hygiene. If your email list contains a high percentage of invalid, inactive, or non-existent email addresses, you might inadvertently be sending to many problematic recipients. These addresses, sometimes referred to as spam traps, can quickly deplete your allocated recipient quota or negatively impact your sender reputation, making receiving servers more stringent with your limits. This is also why some servers might issue a 550 5.4.1 bounce message.

Furthermore, a low or declining sender reputation can exacerbate the problem. When your email domain reputation is poor, recipient servers are more likely to apply stricter limits, even for moderate sending volumes. This is a common issue that can cause emails to go to spam. They may also be more likely to place your sending IP or domain on a blacklist or blocklist if the perceived abusive behavior continues, leading to widespread email rejections.

Common issues

Aggressive sending rate: Sending too many emails to a single domain or recipient within a short timeframe.
Poor list hygiene: Including a large number of invalid or inactive email addresses in your recipient lists.
Low sender reputation: Your IP or domain has a poor reputation, leading recipient servers to apply stricter limits.
Misconfigured lists: Sending to a high concentration of problematic addresses for a specific domain.

Solutions

Implement throttling: Gradually increase your sending volume, especially to new domains or those that previously bounced.
Clean your lists: Regularly remove bounced and unengaged email addresses to improve list quality.
Improve sender reputation: Ensure proper authentication (SPF, DKIM, DMARC) and maintain consistent sending practices.
Verify domains: Double-check the MX records of domains receiving high bounce rates for accuracy.

Troubleshooting and resolving the bounce

To effectively resolve a "Resources restricted - exceeds recipients limit" bounce, start by analyzing your bounce logs. Look for patterns: Is the bounce occurring predominantly with a specific domain, or is it widespread across many domains? Identifying the problematic domains will help you focus your troubleshooting efforts.

Next, implement or adjust your sending rate limits (also known as throttling). Most email service providers allow you to control the speed at which you send emails. For domains experiencing these bounces, try significantly reducing your sending rate. This gives the recipient server time to process the incoming mail without being overwhelmed. You can also review guides on troubleshooting rate limit issues for more detailed steps.

Additionally, clean your email list. Removing invalid or inactive addresses is crucial, as sending to these addresses wastes your sending resources and can negatively impact your sender reputation. Regularly auditing your list to ensure it only contains engaged recipients will improve your overall email deliverability. This proactive approach helps prevent many types of bounces, including those related to recipient limits.

Verifying DNS records for problem domains

Sometimes, the issue isn't just about sending volume but also about the validity of the recipient domain itself, or how your reporting might misinterpret a domain. It is important to confirm that the domains you are sending to actually exist and have valid MX (Mail Exchange) records. A simple DNS lookup can help confirm this. For example, if your bounce reports show issues with "opt-online.net", double-check if it should be "optonline.net" or another similar domain. A hyphen can make all the difference, routing mail to an entirely different, perhaps non-existent, address.

Example dig command for MX record checkBASH

dig MX opt-online.net
;; ANSWER SECTION:
opt-online.net.        300     IN      A       209.18.10.150

If a domain has no MX records or doesn't exist, emails to it will hard bounce, but sometimes a misinterpretation in a temporary bounce message can occur before a full hard bounce is registered. Removing non-existent or typo-ridden addresses from your list will significantly improve your sending efficiency and reduce misleading bounce reports.

Long-term prevention strategies

Beyond immediate troubleshooting, focus on long-term strategies to prevent recurrence of "Resources restricted - exceeds recipients limit" bounces. Building and maintaining a strong sender reputation is paramount. This involves consistent sending volumes, low complaint rates, and avoiding sudden, large spikes in email activity. A good reputation signals to receiving servers that you are a legitimate sender, making them less likely to impose strict limits or blacklist (or blocklist) your messages.

Ensure your email authentication protocols are correctly configured. This includes SPF, DKIM, and DMARC. Proper authentication verifies your identity as a sender, increasing trust with recipient servers and reducing the likelihood of your emails being flagged as suspicious or spam. Servers are more forgiving with well-authenticated mail streams.

Finally, regularly monitor your email deliverability metrics. Keep an eye on your bounce rates, specifically distinguishing between soft and hard bounces, and track your email reputation with major mailbox providers. Early detection of rising bounce rates or other deliverability issues allows for proactive intervention, preventing minor problems from escalating into major blacklisting incidents. This vigilance is a cornerstone of healthy email practices.

Views from the trenches

Best practices

Actively monitor your bounce logs to identify specific domains or patterns where 'resources restricted' bounces occur.

Implement granular sending rate limits per domain or IP to avoid overwhelming recipient servers.

Regularly clean your email lists to remove inactive, invalid, or non-existent addresses.

Maintain a consistent sending volume and avoid sudden spikes in email campaigns.

Ensure all your email authentication protocols (SPF, DKIM, DMARC) are correctly configured.

Common pitfalls

Sending to unverified or old email lists without prior cleaning or re-engagement campaigns.

Ignoring early soft bounce warnings, which can lead to stricter rate limits or blacklisting.

Assuming all 'resources restricted' bounces are the same; some may indicate underlying domain validity issues.

Failing to adapt sending speeds to different recipient domains, as each has unique limits.

Not regularly checking your sender reputation, which influences how recipient servers treat your emails.

Expert tips

For persistent 'resources restricted' bounces to a specific domain, try to reduce your sending rate to an extremely low level initially, then gradually increase it while monitoring bounces.

If a recipient domain appears to be non-existent or has no valid MX records, immediately remove those addresses from your mailing list.

Always verify the exact domain name in bounce messages, as small typos can lead to entirely different delivery issues.

A high soft bounce rate with 'resources restricted' can sometimes mask underlying list quality issues, so investigate your list health.

Consider segmenting your larger email lists to send smaller, more targeted batches, especially to domains with known strict limits.

Expert view

An expert from Email Geeks says that the bounce message indicates sending emails faster than the recipient's server expects.

December 1, 2023 - Email Geeks

Expert view

An expert from Email Geeks notes that checking the domain's MX records is crucial, as some domains causing these bounces may not even exist or are known to be problematic, requiring significantly reduced send limits.

December 1, 2023 - Email Geeks

Maintaining healthy email deliverability

Encountering "Resources restricted - exceeds recipients limit" bounces is a clear signal from recipient mail servers that your sending practices need adjustment. It is a prompt to fine-tune your approach, rather than a permanent rejection. By understanding the underlying causes, such as aggressive sending rates, poor list hygiene, or even overlooked domain typos, you can implement targeted solutions.

Proactive email deliverability management, including strategic throttling, rigorous list cleaning, and consistent monitoring of your sender reputation, will not only resolve these specific bounce issues but also significantly improve your overall email success. This ensures your valuable messages reliably reach the inbox and maintain strong sender relationships.