Why are intermediate sending platform IPs visible in email 'Received' headers and what are the reputation implications?
Michael Ko
Co-founder & CEO, Suped
Published 26 May 2025
Updated 18 Aug 2025
6 min read
When an email is sent, it often travels through a series of servers before reaching its final destination. Each server that handles the email typically adds a Received header, which logs the IP address of the previous server and other routing information. This can sometimes lead to unexpected IP addresses, especially those of intermediate sending platforms, being visible in the email headers.
Understanding why these intermediate IPs are visible and what implications they have for your sender reputation and deliverability is crucial for any email marketer or system administrator. It directly impacts whether your messages land in the inbox or the spam folder.
Understanding email headers and their purpose
Every email carries a hidden trail of its journey in its headers. These headers contain technical metadata that provides a detailed log of the servers involved in the email's transmission. The Received header is one of the most important elements, as it's added by each Mail Transfer Agent (MTA) that processes the message.
Each Received header records key information about the transaction, including the sender's IP address (the previous hop), the recipient's IP address (the current server), the time the email was received, and often the server's hostname. This chain of Received headers essentially maps out the entire path an email takes from its origin to the recipient's inbox. You can learn more about this in the ultimate guide to email headers.
These headers are invaluable for troubleshooting deliverability issues, identifying the true origin of a message, and detecting potential spam or phishing attempts. Without them, it would be incredibly difficult to trace the path of an email or diagnose why it might have been delayed or rejected.
Why intermediate IPs are recorded
The visibility of intermediate sending platform IPs in Received headers is a fundamental aspect of how email infrastructure operates. When you use a third-party platform, like a marketing automation system or a sales engagement tool, to send emails, your messages often go through that platform's servers before being passed to an Email Service Provider (ESP) or directly to the recipient's mailbox provider.
Each of these hops, from your initial sending server to the intermediate platform and then to the final delivery server, legitimately adds its own Received header. This is not something that can typically be hidden or stripped by the sender or even the intermediate platform itself without violating email standards. Mail servers are designed to record the previous server they received mail from for security and traceability.
Email service providers often have a strong interest in revealing the source of the mail they receive. This allows them to differentiate traffic originating from different customers or platforms using their shared infrastructure. If one customer's upstream sending platform has a poor reputation, the ESP wants to isolate that behavior from other customers to protect their overall IP reputation (or blocklist score). This is especially true for shared IP pools, where multiple senders use the same IP addresses.
Reputation implications
The visibility of intermediate IPs has direct implications for your email IP reputation. Mailbox providers (like Google and Microsoft) analyze all visible IPs in the Received headers to determine the trustworthiness of an incoming email. If an intermediate platform has a history of sending unwanted mail, its IPs may be on various blacklists (or blocklists) or have a poor sender score.
This poor reputation can then transfer to your email, even if your primary sending ESP has a good reputation. It's similar to having a bad neighborhood address, even if your house is well-maintained. Mailbox providers might penalize the email's deliverability, leading to messages landing in the spam folder or being outright rejected. This scenario is particularly relevant for shared IP pools.
For dedicated IP addresses, the risk is lower if you maintain strict sending practices, as your reputation is solely tied to your own sending behavior. However, the presence of an intermediate IP that frequently sends spam can still raise red flags. It's a signal that your email has passed through a system associated with undesirable sending practices, which could affect your overall inbox placement.
Shared IP addresses
Exposure: Shared IPs used by multiple senders. Poor reputation of one sender affects all others sharing the IP.
Impact: Higher risk of deliverability issues due to co-tenancy. Intermediate IPs can further complicate this.
This means that even if you're using a top-tier ESP with a solid reputation, the reputation of any intermediate sending platforms you use can still affect your overall deliverability. It underscores the importance of vetting every service in your email sending chain.
Managing your reputation with intermediate platforms
While you cannot typically prevent intermediate IPs from appearing in Received headers, you can take steps to manage your sender reputation effectively. The primary strategy involves being highly selective about the platforms you use to send email.
Prioritize platforms that maintain excellent sending practices, have strong policies against spam, and actively work to keep their IP addresses off blacklists (or blocklists). This due diligence helps ensure that any visible intermediate IPs contribute positively or, at worst, neutrally to your email's perceived trustworthiness. Regular blocklist monitoring can also help you identify if any of your sending IPs, including intermediate ones, have been listed.
Sending platform reputation
Choose platforms that prioritize good sending practices and have a strong focus on deliverability. Avoid those known for permissive policies regarding unsolicited mail, as their shared IPs (and thus, your intermediate hops) will carry a poor reputation.
Views from the trenches
Best practices
Actively monitor all IP addresses in your email's sending path, including intermediate ones, for blocklist appearances and reputation scores to catch issues early.
Always prioritize working with reputable email service providers and third-party sending platforms that have a proven track record of maintaining high deliverability standards.
Ensure that all domains involved in your email sending, whether primary or used by intermediate platforms, are properly authenticated with SPF, DKIM, and DMARC.
Segment your email lists and sending practices based on the nature of the content and recipient engagement, using dedicated IPs for critical streams if possible.
Common pitfalls
Ignoring the reputation of intermediate IPs, assuming only the final sending IP matters, can lead to unexpected deliverability issues and spam folder placement.
Attempting to hide or strip 'Received' headers, which is against email standards and raises red flags with mailbox providers, potentially harming sender trust.
Using cheap or unknown third-party sending tools that have poor IP reputations due to lax sending policies, negatively impacting your email's path.
Failing to conduct regular email deliverability tests across all sending platforms, missing early signs of degraded sender reputation due to intermediate hops.
Expert tips
Implement a consistent DMARC policy across all sending domains to gain visibility into all IP addresses sending email on your behalf, even unexpected ones.
For high-volume senders, consider using dedicated IPs with intermediate platforms to gain more control over your specific sending reputation.
If using shared IPs, ensure your ESP has strong abuse detection and mitigation processes to protect their IP reputation, which indirectly benefits your deliverability.
Educate your team on the importance of email hygiene and legitimate sending practices, as human error can quickly degrade IP reputation regardless of infrastructure.
Expert view
Expert from Email Geeks says the reason for the query will significantly impact the appropriate answer regarding IP visibility in headers.
2024-05-28 - Email Geeks
Expert view
Expert from Email Geeks says that if a sending platform has a bad reputation, it's likely for a good reason, and the recipient mailbox providers might want to use that second Received header to differentiate email streams for reputation management.
2024-05-28 - Email Geeks
Key takeaways
The visibility of intermediate sending platform IPs in email Received headers is a built-in feature of email architecture, designed for traceability and security. While these IPs cannot be hidden, their presence significantly influences your email's reputation and deliverability.
By carefully selecting your sending platforms, maintaining strong email authentication (SPF, DKIM, DMARC), and consistently adhering to best practices, you can mitigate potential negative impacts. Proactive reputation management across your entire email sending infrastructure is key to ensuring your messages consistently reach the inbox.
Google and 
Microsoft) analyze all visible IPs in the Received headers to determine the trustworthiness of an incoming email. If an intermediate platform has a history of sending unwanted mail, its IPs may be on various blacklists (or blocklists) or have a poor sender score.
