Why are recipients exceeding their hourly email limit when BCC is used?
Michael Ko
Co-founder & CEO, Suped
Published 24 Jul 2025
Updated 19 Aug 2025
7 min read
When you send an email with a Blind Carbon Copy (BCC) field, you might assume that it helps you discreetly send messages to multiple recipients without them seeing each other. While this is true from a recipient's perspective, it often leads to a common and frustrating problem: exceeding hourly email limits. Many users find themselves scratching their heads when they receive bounce messages indicating 554 5.2.122 The recipient has exceeded their limit for the number of messages they can receive per hour, even when sending what they believe to be a single email. Let's delve into why this happens and what you can do about it.
How BCC impacts your sending limits
The fundamental reason BCC usage can lead to exceeding hourly limits lies in how mail servers process messages. When you add recipients to the BCC field, your email client (or sending server) still generates a separate copy of the email for each BCC recipient. Even though these recipients are invisible to each other in the email header, each one counts as an individual message delivery attempt by your mail server.
Many email service providers (ESPs), internet service providers (ISPs), and even internal mail systems impose sending rate limits. These limits are typically defined by the number of messages or recipients allowed within a specific timeframe, such as per hour or per day. When you use BCC extensively, you can quickly hit these limits, especially if your recipient list is large. For example, if you send an email to one 'To' recipient and 99 BCC recipients, your mail server is effectively attempting to send 100 individual messages.
A critical issue that can arise, as seen in some real-world scenarios, is when an ESP (or your own mail server) does not properly log these BCC sends. This means that while the email technically counts against your sending limits, the bounce messages might be incorrectly attributed to recipients in the 'To' or 'CC' fields, making diagnosis difficult. It creates a deceptive situation where you see bounce errors for seemingly few recipients, but the actual volume includes hidden BCCs that exceeded the hourly quota.
Why ISPs impose recipient rate limits
Email providers implement sending and receiving limits primarily for security and stability. These measures are designed to combat spam, prevent malicious activities like list bombing (sending a flood of emails to a single address), and ensure the smooth operation of their mail infrastructure. Without such limits, a compromised account could overwhelm the system or target users with unsolicited messages.
Major providers like Google and Microsoft have clear guidelines on their sending limits, which can vary for free consumer accounts versus paid business accounts. For instance, Gmail (consumer) typically limits messages to 500 recipients per day, while Microsoft 365 might have a recipient rate limit of 10,000 recipients per day, but also a rate limit of 30 messages per minute per user.
It is important to remember that these limits apply to the total number of recipients across all messages you send within a given timeframe, not just a single email. So, if you send several emails, each with a large number of BCC recipients, you can quickly hit your cumulative hourly or daily limit. This is often why you see the recipient has exceeded their limit bounce error.
Even if your email is legitimate, mail systems may temporarily rate limit or block further delivery if a recipient's hourly incoming mail quota is exceeded. This acts as a defensive mechanism to prevent inboxes from being flooded, even if the sender has good intentions. Sometimes, it can even catch legitimate email addresses that are commonly made up or shared, like nomail@example.com.
Consequences and prevention strategies
Consistently hitting recipient limits, especially when using BCC for bulk sends, can negatively impact your sender reputation. ISPs and mailbox providers closely monitor sending behavior. High bounce rates, including those due to exceeding recipient limits, signal to them that you might be sending unsolicited mail, potentially leading to your IP address or domain being added to a blacklist (or blocklist). Once blocklisted, your emails may face higher spam filtering, throttling, or outright rejection, severely affecting your overall deliverability.
To prevent these issues, it is essential to adjust your sending strategy. One effective method is to segment your recipient lists into smaller batches and implement sending throttling. This means sending emails in controlled bursts rather than all at once. For example, instead of sending one email to 500 BCC recipients, send 10 emails each to 50 recipients over a longer period. Many email platforms offer features for managing send rates and batching.
Identifying the bounce
Bounce code: Look for 554 5.2.122 or similar messages like "recipient has exceeded their limit" in your bounce logs. These indicate the recipient cannot receive more emails temporarily.
Log review: Examine your ESP or mail server logs for detailed bounce reasons. If the logs are not transparent about BCC recipients, it can complicate troubleshooting.
Preventative measures
Segment lists: Break down large sends into smaller, manageable segments.
Throttling: Implement sending throttling to control the rate of outgoing emails.
Monitor deliverability: Regularly check your deliverability reports for signs of rate limiting or blocklisting.
Alternatives to BCC for bulk sending
For mass communications, especially marketing or transactional emails, relying on BCC is not a recommended practice. While it offers a quick way to hide recipients, it lacks critical features for effective email management and deliverability. Instead, consider using dedicated email sending platforms. These platforms are designed to handle large volumes of email, manage subscriber lists, and automatically adhere to ISP sending limits through advanced throttling mechanisms.
Using BCC for mass sends
Limits: Easily exceeds hourly recipient limits set by mailbox providers, leading to bounces.
Privacy: Hides recipients from each other, but doesn't handle unsubscribes or preferences effectively.
Tracking: No built-in analytics for opens, clicks, or engagement.
Utilizing mailing lists or professional email marketing software ensures that your messages are sent responsibly and efficiently. These tools manage the technical complexities of bulk sending, including compliance with anti-spam regulations, handling bounces, and providing detailed analytics. They also help maintain a good sender reputation, which is crucial for long-term email deliverability. For internal communications, a distribution group or an internal mailing list service is a far superior choice over manual BCCing.
Ensuring your emails get through
Understanding why recipients exceed their hourly email limit when BCC is used boils down to how mail servers count individual recipient deliveries. Each BCC recipient counts towards your sending quota, and exceeding these limits can trigger bounce messages and negatively impact your sender reputation. Moving away from BCC for mass communications and embracing dedicated email sending solutions or properly managed mailing lists is the most effective way to ensure your emails reliably reach their intended inboxes while staying within provider limits.
By adopting these best practices, you can navigate the complexities of email sending limits, reduce bounce rates, and improve your overall email deliverability. Always prioritize responsible sending practices to maintain a healthy sending reputation and ensure your messages get through.
Views from the trenches
Best practices
Always use a dedicated email sending platform for bulk or marketing emails. These platforms handle recipient limits and throttling automatically, preventing common issues.
Segment your recipient lists into smaller batches, especially when sending to a large number of contacts. Distribute sends over time to avoid hourly limits.
Regularly monitor your email bounce logs and delivery reports. Pay close attention to error codes like '5.2.122' to diagnose and address rate limit issues promptly.
Common pitfalls
Relying on the BCC field for mass communication is a common pitfall. Each BCC recipient counts individually against limits, often leading to unexpected bounces.
Assuming that just because BCC hides recipients, it bypasses sending limits. Mail servers still process each BCC recipient as a separate send.
Not understanding the specific sending limits of your email provider or internal mail system. These can vary significantly and impact your delivery.
Expert tips
If your ESP doesn't accurately log BCC recipients in bounces, that's a significant flaw. Push for transparency in logging to properly diagnose issues.
Consider list bombing prevention. Mailbox providers often implement recipient limits to stop scenarios where a single address is flooded with messages.
Custom recipient limits can be set by Microsoft 365 administrators. If you're hitting limits for corporate domains, the recipient's admin might have restrictive settings.
Marketer view
Marketer from Email Geeks says they observed a "recipient has exceeded their limit for the number of messages they can receive per hour" bounce message, seeking clarification on its meaning.
2023-11-03 - Email Geeks
Expert view
Expert from Email Geeks says that many mailbox providers have enforced recipient limits for several years, noting this is a common practice.
