What are the best practices for improving email deliverability with Klaviyo, Microsoft, and Yahoo?
Michael Ko
Co-founder & CEO, Suped
Published 23 Jul 2025
Updated 19 Aug 2025
8 min read
Migrating email platforms can sometimes introduce unexpected deliverability challenges, even when foundational elements like dedicated domains and authentication records (DKIM, DMARC, SPF) are seemingly in place. While the transition to a platform like Klaviyo might offer enhanced segmentation capabilities, it's not uncommon to see a dip in inbox placement, particularly with major mailbox providers like Microsoft and Yahoo. I've seen many businesses face this struggle, experiencing lower open rates, clicks, and revenue despite their best efforts in list hygiene and content optimization.
The key often lies in understanding that each mailbox provider has its own intricate filtering mechanisms and reputation algorithms. What worked seamlessly with a previous email service provider (ESP) might not translate directly, even with the same sending practices in place. It becomes a matter of delving deeper into the nuances of how these providers assess your sending reputation and message quality.
This guide will walk you through the essential best practices tailored for improving your email deliverability specifically with Klaviyo, Microsoft, and Yahoo. We'll cover everything from technical configurations and list management to content strategies and proactive monitoring, ensuring your messages consistently reach the inbox.
The foundation of trust: Authentication and infrastructure
Email authentication, including SPF, DKIM, and DMARC, forms the bedrock of your sender reputation. It tells mailbox providers that your emails are legitimate and haven't been tampered with. While you might have these records set up, it's crucial to verify their correct implementation and ongoing alignment, especially after migrating ESPs. Misconfigurations can severely impact your deliverability to Microsoft and Yahoo.
If you're using dedicated IPs, a proper IP warm-up process is non-negotiable. An aggressive warm-up can quickly land you on a blacklist (or blocklist) and tank your reputation. Even if you followed Klaviyo's recommendations, it's worth reviewing the pacing and volume. For shared IPs, a sudden drop in deliverability might indicate a bad IP pool, and you should request a switch to a healthier one from your ESP.
Remember that both Microsoft and Yahoo rely heavily on these authentication signals to determine if your emails are trustworthy. Ensuring perfect alignment is a continuous effort that directly impacts your sender reputation and deliverability.
This DMARC record, when published in your DNS, instructs receiving mail servers (like Microsoft and Yahoo) not to take action on emails that fail DMARC authentication. It also directs aggregate and forensic reports to the specified email addresses, which are invaluable for monitoring your domain's authentication status and identifying potential issues.
Nurturing your audience for better inbox placement
Even if your technical setup is perfect, poor list quality will inevitably lead to deliverability problems. While buying lists is a clear no-go, issues can arise from other sources. For e-commerce businesses, common acquisition methods include welcome pop-ups and checkout opt-ins. Physical store sign-ups, especially those involving financial incentives, also carry a risk. It's essential to scrutinize every lead source for potential data quality gaps.
I've often seen deliverability issues stemming from sources that introduce invalid addresses, spam traps, or unengaged users. Implementing real-time email verification at the point of collection, even for in-store sign-ups, is a critical step. While some verification tools excel for e-commerce, finding one that integrates seamlessly with your point-of-sale (POS) system can be challenging but is worth the investment. It helps you avoid blacklists (or blocklists) before they happen.
Beyond acquisition, continuous list hygiene is vital. Regularly removing inactive or unengaged subscribers through sunset flows helps maintain a healthy list, signaling to Microsoft and Yahoo that your emails are valued. Actively engaged audiences lead to higher open rates and lower complaint rates, which are critical factors in sender reputation.
Good acquisition practices
Explicit consent: Always use double opt-in for all sign-ups to confirm subscriber interest.
Real-time verification: Integrate email verification tools at point of collection.
Transparent incentives: Clearly state what subscribers will receive when they opt in, even with financial incentives.
Bad acquisition practices
Purchased lists: Never send to bought or scraped email lists, as they are ripe with spam traps.
Unvalidated sign-ups: Allowing unverified email addresses to join your list can lead to high bounces.
Lack of clear expectations: Misleading users about email frequency or content can cause high complaint rates.
Engagement and content strategies
Mailbox providers heavily weigh user engagement and spam complaints. Low open rates, click-through rates, and high complaint rates are red flags that can push your emails to the spam folder. Focusing on engagement means sending relevant content to the right segments of your audience. Monitoring open, click, spam complaint, bounce, and unsubscribe rates, broken out by mailbox provider, is crucial for assessing deliverability.
Klaviyo's powerful segmentation tools allow you to target your most engaged subscribers. If you've recently migrated, consider initially reducing your sending to only the most active segments to rebuild your reputation with Microsoft and Yahoo. Gradually expand your audience as engagement improves. Personalization and relevant content also play a significant role in fostering positive engagement.
Content quality is another huge factor. Spam filters analyze the content of your messages. Avoid spammy words, excessive exclamation points, or overly promotional language that can trigger filters. Mixing in text-only emails and encouraging replies from users can send stronger signals to mailbox providers, indicating genuine two-way communication. For Yahoo email deliverability, consistency in sending is also a best practice.
Proactive monitoring and ISP engagement
To truly understand your deliverability performance, especially with Microsoft and Yahoo, direct access to their postmaster tools is invaluable. Microsoft's Smart Network Data Services (SNDS) and Google Postmaster Tools (GPT) provide data on complaint rates, reputation, and even spam trap hits. While Klaviyo might monitor these on your behalf, having direct access gives you the full picture.
These tools can help diagnose specific issues related to Microsoft Outlook, Hotmail, and Yahoo. For instance, registering IPs in SNDS and JMRP is a crucial step for better Microsoft deliverability. These tools show you complaint rates, which are direct feedback from users marking your emails as spam, a significant factor in your reputation.
Don't hesitate to contact Microsoft and Yahoo postmaster teams directly if you suspect ongoing issues. While Microsoft can be a crapshoot, the Yahoo team is generally responsive and helpful. Be persistent if Microsoft initially claims no issues, as a follow-up often reveals a mitigated problem.
Persistence with Microsoft Support
If Microsoft replies to your ticket stating there are no issues, it's a good practice to reply again, asserting that problems persist. It's surprisingly common for them to then investigate further and confirm a mitigation action. This small act of persistence can often yield positive results in resolving deliverability blocks.
Continuous monitoring and adaptation
Consistent monitoring of your email deliverability metrics is crucial. Don't just look at overall open rates, but segment them by mailbox provider. If Microsoft and Yahoo are specific pain points, track their metrics closely. Tools like Google Postmaster Tools can offer valuable insights into your sender reputation and potential issues.
If, after all these steps, you still face persistent issues, consider whether your email sending strategy aligns with the specific expectations of Microsoft and Yahoo. Sometimes, even subtle shifts in content, frequency, or segmentation can have a significant impact. It's a continuous learning process to maintain optimal deliverability across all providers.
Views from the trenches
Best practices
Implement email verification on all sign-up forms, including physical store opt-ins, to prevent invalid addresses.
Segment your audience aggressively based on engagement, starting with the most active users after a platform migration.
Prioritize text-only emails and encourage replies to signal active engagement to mailbox providers.
Continuously monitor your sender reputation and deliverability rates through Microsoft SNDS and Google Postmaster Tools.
Common pitfalls
Assuming deliverability practices from a previous ESP will translate directly to a new platform like Klaviyo.
Neglecting real-time email verification for new sign-ups, especially those from offline channels.
Failing to adapt email content and sending patterns to the specific filtering behaviors of Microsoft and Yahoo.
Not being persistent with ISP postmaster teams, particularly Microsoft, when initial requests for assistance are dismissed.
Expert tips
If using dedicated IPs, ensure a gradual and consistent warm-up. Rushing the process can lead to immediate blacklisting (or blocklisting) and reputation damage.
Leverage the full capabilities of Klaviyo's segmentation to send highly targeted and engaging content, improving your overall sender reputation.
Beyond technical setup, content relevance and user experience are paramount. Personalize your messages to increase opens and clicks.
Consider a phased approach to re-engaging your audience after a migration. Start with high-engagement segments and slowly broaden your reach.
Marketer view
Marketer from Email Geeks says that if you're doing all the technical setup correctly, issues are most likely due to content or targeting. They emphasize monitoring open rates and bounces to understand the problem.
2024-04-09 - Email Geeks
Expert view
Expert from Email Geeks says that many organizations are experiencing deliverability challenges with Microsoft, and that segmentation and audience selection are key, advising to ensure the audience is active and engaged.
2024-04-09 - Email Geeks
Achieving lasting inbox success
Improving email deliverability with Klaviyo, Microsoft, and Yahoo is a multifaceted challenge that requires attention to technical setup, audience quality, content relevance, and continuous monitoring. There is no single magic bullet, but rather a combination of best practices that, when consistently applied, will yield significant improvements. The journey often involves meticulous review of existing practices and a willingness to adapt.
By prioritizing robust authentication, maintaining a clean and engaged subscriber list, crafting compelling content, and actively utilizing postmaster tools, you can build a strong sender reputation and ensure your emails consistently reach their intended recipients' inboxes. Remember that deliverability is an ongoing process, not a one-time fix.
Klaviyo might offer enhanced segmentation capabilities, it's not uncommon to see a dip in inbox placement, particularly with major mailbox providers like 
Microsoft and 
Yahoo. I've seen many businesses face this struggle, experiencing lower open rates, clicks, and revenue despite their best efforts in list hygiene and content optimization.
Monitoring open, click, spam complaint, bounce, and unsubscribe rates, broken out by mailbox provider, is crucial for assessing deliverability.
Microsoft's Smart Network Data Services (SNDS) and Google Postmaster Tools (GPT) provide data on complaint rates, reputation, and even spam trap hits. While Klaviyo might monitor these on your behalf, having direct access gives you the full picture.
Google Postmaster Tools can offer valuable insights into your sender reputation and potential issues.
