What to do about blocked bounces on first send with a new IP?
Michael Ko
Co-founder & CEO, Suped
Published 20 May 2025
Updated 16 Aug 2025
7 min read
Starting with a new IP address for email sending should be a smooth process, but sometimes, even with low volumes on your first send, you encounter a frustrating issue: blocked bounces. This is especially perplexing when major mailbox providers like Gmail, Yahoo, and Hotmail are accepting your mail, but smaller, specific domains are not.
The common bounce message, "Blocked due to spam or sender reputation issue," can be alarming, making you wonder what went wrong right out of the gate. It's a clear signal that the receiving server, for whatever reason, views your new IP as suspicious or untrustworthy.
This guide will walk you through the immediate steps to take, the underlying causes, and strategies to prevent such issues from recurring as you continue to build your sending reputation.
Understanding the problem
When your brand new IP address encounters blocked bounces on its first send, the core problem is often a lack of established reputation. Mailbox providers and spam filters, especially those used by smaller, stricter domains, are inherently cautious of unknown sending IPs. They prefer to see a consistent history of good sending behavior.
These systems rely on various factors to assess an IP's trustworthiness, and a new IP has none of that history. This can lead to your emails being immediately flagged as spam or blocked, even if your content is legitimate and your list is clean. It's a protective measure on their part, designed to prevent bad actors from quickly onboarding new IPs and blasting spam.
Another factor can be the shared IP environment, even if it's a dedicated IP from your email service provider. Sometimes, IP ranges can be pre-flagged or carry residual reputation from previous users. This can lead to your IP being listed on a public blacklist or blocklist before you even send your first email. Understanding how email blacklists actually work is key to troubleshooting.
Initial troubleshooting and diagnostics
The first step is to methodically investigate the bounces to identify patterns and specific reasons. While the general message is "spam or sender reputation," the nuances can point you to the actual root cause.
Check for any immediate blocklist (or blacklist) listings of your new IP. Many public blacklists update frequently, and a new IP can quickly land on one if initial sends trigger spam traps or high complaint rates. Knowing what happens when your IP gets blocklisted can help you understand the impact.
Next, analyze the domains that are blocking your emails. As observed, large providers might be fine, but smaller domains are problematic. This often points to specific spam filters or custom configurations. You might need to check the Mail Exchanger (MX) records for these domains to see if they are using a common anti-spam service like Proofpoint, which are known for their strict filtering. B2B email sends often face these issues.
Immediate actions
Immediately halt sending to the domains that are bouncing. Continuing to send will only worsen your reputation and dig you deeper into a blocklist hole.
Check public blacklists for your IP address. Many services offer free IP blacklist checks. If listed, gather details for de-listing requests.
Review your email content. Look for any elements that might appear spammy, such as excessive images, shorteners, or generic unsubscribe links. Sometimes, the content itself can trigger filters, regardless of the IP.
Strategic approaches for new IPs
A new IP address requires careful warming up to build a positive reputation with mailbox providers. This involves sending emails in gradually increasing volumes to engaged recipients. If you encounter blocks on your first send, it's a sign that your warming strategy may need adjustment or was too aggressive for certain recipients.
For the domains that blocked your initial sends, you might need to try reaching out to their administrators directly. This is particularly relevant for the Apple domains (icloud.com, me.com, mac.com) and other specific company domains. They may have a postmaster address or a process for requesting de-listing or whitelisting of your IP. For general bounces and blocks, Google provides tips on what to do when your IP is blocked.
Long-term, focus on meticulous list hygiene. Sending to invalid or unengaged addresses from the start can quickly destroy your new IP's reputation. Ensure your mailing list is clean and uses a double opt-in process. This minimizes bounces and spam complaints, allowing you to warm up new IP addresses effectively. You can learn more about handling bounced emails from authoritative sources.
Consider implementing blocklist monitoring for your IP. This proactive measure alerts you immediately if your IP gets listed on any major or minor blocklists, allowing for quicker intervention. Addressing IP blocklists during warmup is critical for new IPs.
Content and authentication considerations
Content quality plays a significant role in deliverability, especially for new IPs with unestablished reputations. Filters scrutinize content more heavily when the sender is unknown. Even seemingly innocuous elements can trigger spam filters.
This includes the use of third-party tracking links, URL shorteners, or even images hosted on domains with poor reputations. When starting with a new IP, it's advisable to keep your email content as clean and straightforward as possible, focusing on plain text or minimal HTML with direct, well-known links. Avoid anything that might be perceived as a stealthy or suspicious tactic.
Ensuring proper email authentication is also paramount. SPF, DKIM, and DMARC records signal to receiving servers that your emails are legitimate and prevent spoofing. While these don't directly prevent a new IP blocklist issue, they are foundational for good deliverability and will help build trust over time. Make sure your DMARC policy is correctly configured.
Views from the trenches
Best practices
Start with smaller segments of your most engaged subscribers to build initial positive sending reputation.
Continuously monitor your IP's reputation on various blocklists and address any listings promptly.
Maintain pristine list hygiene, removing unengaged or invalid email addresses regularly to prevent bounces.
Implement a slow and steady IP warming schedule, increasing volume gradually over weeks, not days.
Engage directly with postmasters of domains that frequently block your emails, especially niche ones.
Common pitfalls
Sending to large, unsegmented lists immediately, especially those with unknown engagement levels.
Ignoring bounce messages and continuing to send to blocked addresses, further damaging your IP's reputation.
Using generic or low-reputation link shorteners or third-party tracking on new IPs.
Neglecting to monitor blocklists or email authentication records during the IP warmup phase.
Attempting to send high volumes to domains with strict filtering without prior warm-up or direct contact.
Expert tips
Segment your list carefully for initial sends, prioritizing highly engaged recipients.
Check MX records of problematic domains to identify specific anti-spam services they use, such as Proofpoint.
Suppress all addresses that hard bounce from your lists immediately to protect your sender reputation.
Ensure your content is clean: avoid suspicious links, excessive images, or spammy keywords for initial sends.
A gradual increase in volume to active recipients helps build trust with ISPs and avoids triggering spam filters.
Marketer view
Marketer from Email Geeks says they started with a new SFMC dedicated IP and saw blocked bounces on iCloud, me.com, and mac.com along with other single-subscriber domains. They are unsure how to handle the one-off domains.
2023-05-01 - Email Geeks
Marketer view
Marketer from Email Geeks suggests that Apple domains often use Proofpoint, and reaching out to Proofpoint might be a solution for these blocked bounces. Checking the new IP against Proofpoint's IP lookup is also recommended.
2023-05-01 - Email Geeks
Moving forward with a healthy IP
Encountering blocked bounces on your first send with a new IP is certainly a frustrating experience, but it's a common hurdle in email deliverability. The key is to respond strategically and methodically, rather than reacting with panic or sending more emails, which will only exacerbate the issue.
By understanding the reasons behind these initial blocks (often lack of reputation or strict filters like Proofpoint), taking immediate action to pause sends to problematic domains, and implementing a robust, patient IP warming and list hygiene strategy, you can overcome these challenges. Proactive blocklist monitoring and engaging with postmasters when necessary will solidify your sender reputation.
Building a solid sender reputation takes time and consistent effort. Patience, combined with a commitment to best practices in email marketing, will ultimately lead to higher inbox placement rates and successful email campaigns from your new IP address.
Proofpoint, which are known for their strict filtering. B2B email sends often face these issues.
Apple domains (icloud.com, me.com, mac.com) and other specific company domains. They may have a postmaster address or a process for requesting de-listing or whitelisting of your IP. For general bounces and blocks, Google provides tips on what to do when your IP is blocked.
