Why is Hotmail rate limiting my transactional emails due to IP reputation?
Matthew Whittaker
Co-founder & CTO, Suped
Published 14 Jul 2025
Updated 15 Aug 2025
8 min read
It can be incredibly frustrating when your transactional emails, which are critical for your business operations, suddenly get rate limited by Hotmail or Microsoft Outlook. The error message, often citing "temporarily rate limited due to IP reputation", can be puzzling, especially when you're confident you're not sending spam. I've seen this issue many times, and it typically points to how Hotmail's filters perceive your sending IP address.
This isn't about the content of a single email, but rather the overall trust Hotmail places in your sending infrastructure. When they rate limit you, it means they're intentionally slowing down, or even rejecting, your emails because your IP's reputation has flagged their systems. This protective measure is designed to prevent spam and ensure the best experience for their users, even if it inadvertently impacts legitimate senders.
Understanding the nuances of IP reputation and Microsoft's filtering mechanisms is key to resolving this problem. It requires a systematic approach to identify the root cause and implement long-term solutions. Let's delve into why this happens and what steps you can take to get your transactional emails flowing smoothly again.
Why IP reputation matters
IP reputation is essentially a trust score assigned to your sending IP address by internet service providers (ISPs) and email providers like Outlook and Hotmail. This score is dynamic and influenced by various factors, including your sending history, recipient engagement, and compliance with email best practices. A good IP reputation signals that you're a legitimate sender, while a poor one suggests potential spam or malicious activity.
Microsoft, in particular, has sophisticated filtering systems that constantly evaluate incoming mail. They look at the IP address, the domain reputation, and numerous other signals to decide whether to accept, reject, or rate limit an email. When an IP's reputation drops, even for transactional emails, they implement rate limiting to protect their users from potential harm. This is clearly articulated in their documentation, which states that an IP address might be temporarily rate limited due to reputation issues, often accompanied by specific error codes like S775 or S843, as explained in their support documentation.
It's important to differentiate between transactional and marketing emails in your sending strategy. While both types of emails contribute to your overall IP reputation, transactional emails are often time-sensitive and critical. If your transactional emails are impacted, it's a serious sign that your sender reputation is taking a hit, and it requires immediate attention. You can find more details on why Microsoft might be rate limiting email sends for some customers by reading our guide on why Microsoft rate limits.
Common causes of poor IP reputation
Even if you're only sending transactional emails, several factors can negatively impact your IP reputation and lead to Hotmail rate limiting. Identifying these causes is the first step toward resolution. I've observed that some common culprits include:
Spam complaints: Even a small number of users marking your transactional emails as spam can significantly damage your reputation. This might happen if recipients don't recognize the sender or the email's purpose.
High bounce rates: Sending to invalid or non-existent email addresses leads to hard bounces, which tell ISPs that your list hygiene is poor, affecting your IP reputation.
Sudden volume spikes: If you suddenly send a much larger volume of email than usual from a given IP, especially if it's a new or recently inactive IP, Hotmail might see this as suspicious behavior and rate limit you. This is a classic indicator of a compromised sender or spamming activity. Our guide on what causes temporary rate limiting due to IP reputation covers this in more detail.
Low engagement: If recipients aren't opening or clicking your emails, it sends a negative signal to Hotmail's filters. Even for transactional emails, engagement matters. You can understand more about this topic in our article why your emails are going to spam.
Spam trap hits: Sending to a spam trap, an email address used by ISPs to catch spammers, is a severe blow to your reputation. These can be old, inactive addresses that have been repurposed. Our guide to how email blocklists work has more information.
It's also worth noting that if your IP address lands on a public or private blacklist (or blocklist), it will severely hinder your deliverability, leading to rate limiting or outright rejection. You can use Suped's blocklist checker to see if your IP is listed. Even if you're sending legitimate transactional mail, if it's coming from an IP that has been compromised or abused in the past, you'll face problems.
How to diagnose and address the issue
When you encounter a rate limiting message from Hotmail or Outlook, the first step is to diagnose the problem. The error message often includes a link to Microsoft's Postmaster Tools. This is your go-to resource for understanding your IP and domain reputation with Microsoft. If you're encountering general deliverability issues with Microsoft or Hotmail, you can also check our guide on why your emails are having deliverability issues.
Typical problems
Low sender reputation: Due to high complaints, bounces, or spam trap hits.
Sudden increase in volume: Hotmail may throttle if new, high-volume sending patterns appear.
Shared IP issues: If you use a shared IP, other senders' poor practices can affect you.
Practical steps to take
If your IP address has been temporarily blocked (or blacklisted) by Hotmail (Outlook), you can use their specific delisting form. It's often linked directly within the bounce message. Make sure to provide all requested information accurately. In some cases, a temporary block might clear on its own within a few hours or days if the problematic sending stops. However, relying on this is not a sustainable solution.
I also recommend reviewing your sending practices. Are you sending to an engaged audience? Is your list clean? Have you recently acquired new subscribers? Implement strict list hygiene to remove invalid addresses, and consider using CAPTCHA on web forms to prevent malicious sign-ups that could lead to spam trap hits or high bounce rates. For deeper insights into your IP's status, use a blocklist checker to confirm if your IP is listed on any public blacklists.
Check Postmaster Tools: Monitor your IP and domain reputation for Hotmail and Outlook.
Delisting request: Submit a request through the Microsoft sender information for delisting.
Review logs: Look for high bounce rates, spam complaints, or unusual sending patterns.
Rebuilding your sender reputation
Rebuilding your sender reputation with Hotmail (Outlook) is a process that requires consistent effort and adherence to best practices. It's not a quick fix, but a sustained commitment to good email hygiene. You can read more about how to resolve Microsoft email delays due to IP reputation and recipient interaction by checking our dedicated article on the topic: how to resolve Microsoft email delays.
First, ensure your email authentication protocols are properly configured. This includes SPF, DKIM, and DMARC. These records verify that your emails are legitimate and prevent spoofing, which helps build trust with ISPs. Microsoft heavily relies on these protocols for filtering. Our simple guide to DMARC, SPF, and DKIM provides a good starting point. Here's an example of a simple SPF record:
SPF record exampledns
v=spf1 include:_spf.example.com ~all
Second, maintain consistent sending volumes. If you have to send a large batch of emails after a period of inactivity, gradually increase your volume over several days to warm up your IP address. This tells Hotmail that your sending patterns are predictable and not indicative of a sudden spam surge. This concept is also vital for why Gmail might rate limit your emails after low sending volume.
Finally, prioritize recipient engagement and feedback loops. Encourage recipients to add your email address to their contacts, and make it easy for them to manage their preferences or unsubscribe if they no longer wish to receive your emails. Regularly review your Postmaster Tools data for feedback. A high email reputation is built on consistent positive interactions and low complaint rates.
Views from the trenches
Best practices
Maintain a clean email list by regularly removing invalid or inactive addresses to reduce bounce rates.
Implement robust email authentication (SPF, DKIM, DMARC) to verify your sending identity.
Segment your email sending by type, separating transactional emails from marketing campaigns.
Warm up new or inactive IP addresses gradually to build a positive sending reputation over time.
Common pitfalls
Ignoring bounce messages and continuing to send to invalid email addresses.
Not monitoring your IP reputation and failing to use Postmaster Tools for feedback.
Sending sudden, large volumes of email without prior IP warming or established reputation.
Underestimating the impact of user complaints, even for legitimate transactional emails.
Expert tips
Use a dedicated IP address for transactional emails to isolate their reputation from marketing sends.
Enroll in Microsoft's Junk Mail Reporting Program (JMRP) to receive spam complaints directly.
Ensure your web forms are protected with CAPTCHA to prevent spambot sign-ups that can generate bad emails.
Carefully analyze Postmaster Tools data, focusing on complaint rates and reputation scores to identify trends.
Expert view
Expert from Email Geeks says that the immediate cause of rate limiting is Hotmail's assessment of the IP reputation, and it is beneficial to complete any linked forms from the bounce message.
2020-07-01 - Email Geeks
Expert view
Expert from Email Geeks notes that if your mailstream has a poor reputation with recipients, it will be throttled.
2020-07-01 - Email Geeks
Ensuring reliable transactional email delivery
Being rate limited by Hotmail due to IP reputation can be a daunting challenge, especially when dealing with critical transactional emails. However, it's a solvable problem that hinges on understanding and improving your sender reputation. It involves proactive monitoring, diligent list management, and adherence to email best practices.
By consistently authenticating your emails, managing your sending volume, and prioritizing recipient engagement, you can rebuild trust with Hotmail and ensure your important transactional emails reach their intended recipients without interruption. It's a continuous effort, but one that is essential for maintaining robust email deliverability.
Microsoft Outlook. The error message, often citing "temporarily rate limited due to IP reputation", can be puzzling, especially when you're confident you're not sending spam. I've seen this issue many times, and it typically points to how Hotmail's filters perceive your sending IP address.
Outlook and Hotmail. This score is dynamic and influenced by various factors, including your sending history, recipient engagement, and compliance with email best practices. A good IP reputation signals that you're a legitimate sender, while a poor one suggests potential spam or malicious activity.
email reputation is built on consistent positive interactions and low complaint rates.
