Should I switch to a dedicated IP address for Hubspot emails to avoid Outlook quarantine issues?
Michael Ko
Co-founder & CEO, Suped
Published 7 Jun 2025
Updated 17 Aug 2025
9 min read
Many email senders using HubSpot face the challenge of emails landing in the Outlook quarantine, even with seemingly solid deliverability. This often leads to questioning whether switching from a shared IP address to a dedicated one can mitigate these issues. It's a common dilemma, particularly when experiencing intermittent problems with a specific inbox provider like Outlook (or Office 365).
The immediate thought is that a shared IP might be the culprit. On a shared IP, your sending reputation is influenced by other users on the same IP. If one user engages in poor sending practices, it can negatively affect everyone, potentially leading to blocklistings or increased spam filtering for legitimate senders. This shared reputation impact is a strong argument for considering a dedicated IP.
However, the decision to move to a dedicated IP is not always straightforward. While it offers greater control over your sender reputation, it also comes with responsibilities, such as IP warming and direct accountability for deliverability. This article explores whether a dedicated IP is the right solution for HubSpot users experiencing Outlook quarantine issues and what other factors might be at play.
Understanding shared vs dedicated IP addresses
Many email service providers (ESPs) like HubSpot offer both shared and dedicated IP addresses for sending emails. Shared IPs are the default for most users, especially those with lower sending volumes. These IPs are used by multiple clients, and the collective sending behavior impacts the IP's reputation. If one sender on the shared IP gets blocklisted (or blacklisted) due to spam complaints, it can affect others.
Dedicated IPs, conversely, are exclusively assigned to a single sender. This means your email sending reputation is entirely your own, giving you more control over your deliverability. However, this also implies that any negative sending practices (such as sending to unengaged recipients or high bounce rates) will directly impact your IP's reputation, without the buffer of other senders' positive behavior. This is why a dedicated IP requires careful management and consistent sending practices.
For HubSpot users sending around 50,000 emails per week (or 200,000 per month), the volume is often sufficient to consider a dedicated IP. While some experts recommend a minimum of 100,000 emails per month, a consistent volume like this allows for proper IP warming and the establishment of a solid individual reputation. HubSpot themselves acknowledge that dedicated IPs are a good fit for high-volume senders. However, it's crucial to understand that simply having a dedicated IP doesn't automatically solve all deliverability woes.
Shared IP address
Reputation shared: Deliverability is affected by the sending practices of all users on the IP.
Less control: Your reputation is partially outside your direct influence.
No warming needed: The ESP manages the IP reputation and warming.
Cost-effective: Often included with standard plans, no additional fees.
Dedicated IP address
Full control: Your sending reputation is solely your responsibility.
Requires warming: New IPs need to be warmed up gradually to build trust with ISPs.
Volume dependent: Best for consistent, high-volume senders.
Higher cost: Often an add-on with an additional fee.
The impact of IP reputation on Outlook deliverability
When emails from HubSpot are consistently sent to Outlook's (or Office 365) quarantine, it often points to a complex interplay of factors, not just the IP address. While IP reputation is certainly a component, modern inbox providers increasingly rely on domain reputation and content analysis. Microsoft's Defender for Office 365, in particular, uses advanced machine learning to identify and quarantine suspicious emails. This system often flags new or unusual domains appearing in email headers and bodies, rather than solely focusing on the sending IP.
This means that even if you switch to a dedicated IP, if your content or domain practices are problematic, your emails could still end up in quarantine. For instance, if your emails contain links to newly established or previously unverified domains, or if the content triggers spam filters, the IP change alone may not resolve the issue. It's why many experts suggest that content is a more likely culprit for intermittent quarantine issues, especially when email authentication like DMARC is already properly configured.
A dedicated IP can give you more control, but it doesn't bypass the sophisticated filters of Microsoft 365. The reputation of your sending domain remains paramount. If your domain has a low reputation, or if it's new and hasn't been warmed up effectively, emails can still face deliverability challenges, including being sent to the quarantine. Regular monitoring of your domain reputation is essential, regardless of your IP setup.
Understanding Outlook's quarantine triggers
Microsoft Outlook (Office 365) email filtering is highly dynamic and uses advanced algorithms that consider many signals, including IP reputation, domain reputation, email content, and sender authentication (SPF, DKIM, DMARC). Quarantine is often triggered by perceived suspicious activity rather than just a blanket blocklist (or blacklist) of an IP.
Domain reputation: A strong, positive domain reputation is critical. If your domain has a history of high spam complaints or hasn't been properly authenticated, it can lead to quarantine.
Content analysis: Emails with suspicious links, unusual formatting, or content patterns common in spam are often flagged. This includes links to new or unfamiliar domains within the email body or headers.
While a dedicated IP might not be a magic bullet for all Outlook quarantine issues, it certainly offers benefits for HubSpot users with consistent sending volumes. As mentioned earlier, a volume of around 50,000 emails per week (200,000 per month) is generally considered sufficient to warrant a dedicated IP. This volume allows you to establish and maintain a healthy sending reputation on your own IP, without being affected by the sending habits of other users on a shared IP.
The key benefit of a dedicated IP is the direct control you gain over your reputation. If you maintain good sending practices, keep your lists clean, and send engaging content, your dedicated IP's reputation will reflect that. This can lead to more predictable deliverability over time, and it allows for stronger alignment between your sending domain and IP, which ISPs favor. This is especially true for HubSpot customers who want more control over their email deliverability.
However, it's crucial to understand that a dedicated IP requires a proper IP warming process. You cannot simply switch and expect immediate perfect deliverability. The new IP needs to build a sending history and trust with inbox providers gradually. Failing to warm up your IP can actually worsen your deliverability in the short term, as unseasoned IPs are often viewed with suspicion by spam filters. For more on this, consider when a new dedicated IP addresses email sending issues.
Considerations for switching to a dedicated IP
Sending volume: Ensure consistent, high enough volume to maintain a good reputation. Inconsistent or low volume can lead to a 'cold' IP.
Reputation management: You become fully responsible for monitoring and maintaining your IP's reputation, including avoiding blocklists (or blacklists).
Cost: HubSpot's dedicated IP is an additional paid add-on.
Beyond IP: Other factors affecting Outlook deliverability
While a dedicated IP can certainly be a valuable asset for email deliverability, especially for achieving full branding and gaining more control, it's rarely the sole solution to quarantine issues, particularly with Microsoft Office 365. Many experts indicate that Office 365's machine learning for Defender focuses heavily on domain-level reputation and content analysis rather than just the sending IP.
This means that even with a dedicated IP, if your emails are consistently landing in quarantine, you should investigate other factors. Key areas to review include: your email content (are there suspicious links or spammy phrases?), your email authentication records (SPF, DKIM, and DMARC should be correctly configured and aligned), and the health of your email list (are you sending to unengaged or invalid addresses?). HubSpot itself states that a dedicated IP does not guarantee deliverability if sending practices are poor.
For specific issues with Office 365 quarantine, it's often a domain-level event. Microsoft Defender may flag new domains present in the email's headers or body. If you recently added new domains or changed subdomains for tracking, these could be triggers. In such cases, testing small batches of emails with these domains is advisable to identify and address the issue. Additionally, recipients experiencing consistent quarantining should be encouraged to contact their Office 365 administrator to request remediation or allowlisting. This collaborative approach can often resolve persistent quarantine problems more effectively than an IP change alone.
Views from the trenches
Best practices
Maintain clean email lists by regularly removing unengaged subscribers and invalid addresses to improve sender reputation.
Consistently send emails at a predictable volume to help build and maintain a strong reputation for your dedicated IP.
Ensure all email authentication records (SPF, DKIM, DMARC) are correctly configured and aligned with your sending domain.
Regularly monitor your domain and IP reputation using tools like Google Postmaster Tools and other monitoring services.
Gradually warm up a new dedicated IP by sending low volumes of email initially and slowly increasing over time.
Common pitfalls
Assuming a dedicated IP will automatically solve all deliverability issues without addressing underlying content or list quality problems.
Failing to properly warm up a new dedicated IP, which can lead to worse deliverability than a shared IP.
Neglecting email authentication, leading to emails failing SPF, DKIM, or DMARC checks, especially with providers like Microsoft.
Sending emails with inconsistent content or links to new, unverified domains, which can trigger spam filters.
Ignoring recipient engagement and continuing to send to inactive subscribers, which negatively impacts your sender score.
Expert tips
For Office 365 quarantine issues, investigate all domains in the email header and body, as Microsoft Defender's ML often flags new or suspicious domains.
A dedicated IP provides greater control and branding opportunities, but active management of your sending practices remains essential.
If issues are intermittent and DMARC is set up, content is often the primary reason for emails being quarantined.
Engage recipients' Office 365 administrators for remediation if specific users are consistently impacted by quarantine.
While volume is a factor, focus on the quality of your sending practices more than just the quantity of emails sent.
Expert view
Expert from Email Geeks says that a volume of around 50,000 emails per week is enough to support a dedicated IP. While Outlook (or Office 365) is improving at handling shared senders, a dedicated IP allows for more direct management of one's reputation. If sender practices are solid, success on a dedicated IP is likely.
2024-02-14 - Email Geeks
Expert view
Expert from Email Geeks says that for Office 365 quarantine specifically, it's often a domain-level event where Microsoft Defender's machine learning marks new domains in the header and body. It's recommended to test new domains with small sends and verify quarantine status. Dedicated IPs are a plus for avoiding shared IP 'prop wash' and enabling full branding.
2024-02-14 - Email Geeks
Final thoughts on your IP decision
For HubSpot users experiencing intermittent Outlook quarantine issues, switching to a dedicated IP address can be a beneficial step, especially if you have a consistent sending volume of around 50,000 emails per week or more. It provides greater control over your sender reputation and allows for more robust branding. However, it's important to approach this decision with a comprehensive understanding of email deliverability.
A dedicated IP is not a standalone solution for all deliverability challenges. Microsoft Office 365's sophisticated filtering relies heavily on domain reputation and content, meaning that proper email authentication (SPF, DKIM, DMARC), maintaining clean lists, and crafting engaging, non-spammy content remain critical. Failing to properly warm up a new dedicated IP can even exacerbate existing problems.
Ultimately, if you decide to make the switch, ensure you have a solid plan for IP warming and ongoing reputation management. Combine this with vigilant monitoring of your email metrics and an understanding of Outlook's filtering nuances to achieve consistent inbox placement and avoid quarantine issues.
HubSpot face the challenge of emails landing in the Outlook quarantine, even with seemingly solid deliverability. This often leads to questioning whether switching from a shared IP address to a dedicated one can mitigate these issues. It's a common dilemma, particularly when experiencing intermittent problems with a specific inbox provider like Outlook (or Office 365).
Office 365) quarantine, it often points to a complex interplay of factors, not just the IP address. While IP reputation is certainly a component, modern inbox providers increasingly rely on domain reputation and content analysis. Microsoft's Defender for Office 365, in particular, uses advanced machine learning to identify and quarantine suspicious emails. This system often flags new or unusual domains appearing in email headers and bodies, rather than solely focusing on the sending IP.
Outlook (Office 365) email filtering is highly dynamic and uses advanced algorithms that consider many signals, including IP reputation, domain reputation, email content, and sender authentication (SPF, DKIM, DMARC). Quarantine is often triggered by perceived suspicious activity rather than just a blanket blocklist (or blacklist) of an IP.
contact their Office 365 administrator to request remediation or allowlisting. This collaborative approach can often resolve persistent quarantine problems more effectively than an IP change alone.
