How to improve B2B email deliverability and avoid spam folders when nurturing customers?
Matthew Whittaker
Co-founder & CTO, Suped
Published 18 Apr 2025
Updated 19 Aug 2025
8 min read
Getting B2B emails into the inbox, especially for customer nurturing, can feel like navigating a maze. Unlike B2C where engagement metrics often reign supreme, B2B email deliverability faces additional hurdles, primarily the stringent spam filters and security protocols of corporate networks. It's a common frustration to see low open rates or hear customers complain they aren't receiving your crucial updates, even when your internal deliverability stats seem fine. I've seen many businesses struggle with this, particularly when their sending domain for marketing differs from their main corporate domain.
The challenge is amplified because these aren't unsolicited emails, they're meant for existing customers. They are vital for onboarding, product announcements, and providing value that keeps customers engaged with your system. When these messages go missing, it creates a poor customer experience and undermines your nurturing efforts.
My goal here is to break down the core reasons why your B2B nurturing emails might be landing in the spam folder and provide actionable strategies to ensure they consistently reach your customers' inboxes. We'll cover everything from technical setup to content best practices, helping you improve your email deliverability rates.
Prioritise sender reputation and domain health
Your sender reputation is the bedrock of good email deliverability. Internet service providers (ISPs) and corporate email systems (like those from Microsoft) use it to decide whether your emails are trustworthy. A strong sender reputation signals that you are a legitimate sender and helps your emails bypass spam filters. Conversely, a poor reputation can lead to your emails being marked as spam or even blocked entirely. This applies to both your IP address and your sending domain.
For B2B nurturing, maintaining a separate sending domain from your primary corporate domain is common, but it requires careful management. If this sending domain builds a poor reputation, it won't impact your main business communications, but your nurturing campaigns will suffer. It's crucial to monitor the health of this dedicated domain.
Understanding domain reputation
Your domain's reputation is built over time based on various factors, including bounce rates, spam complaint rates, and engagement metrics. High bounce rates or frequent spam complaints, even if only 3% as mentioned by a user in the Slack discussion, can severely damage your domain's standing with mailbox providers. It's an important factor to consider when your emails go to spam or when you're seeking to improve your email reputation and deliverability.
To protect your sender reputation, always warm up new sending domains or IPs gradually. This involves starting with small email volumes to highly engaged subscribers and slowly increasing volume over time. Sudden spikes in sending volume can trigger spam filters, regardless of your content. This practice is vital for building a positive sending history.
Implement robust email authentication protocols
Email authentication is non-negotiable for B2B deliverability. SPF, DKIM, and DMARC records prove to receiving servers that your emails are legitimate and haven't been tampered with. Without these, your emails are far more likely to be flagged as suspicious or spam, especially by corporate spam filters looking to protect their users from phishing and spoofing.
SPF: Sender Policy Framework specifies which mail servers are authorized to send emails on behalf of your domain. If an email comes from a server not listed in your SPF record, it could be rejected or marked as spam.
DKIM: DomainKeys Identified Mail adds a digital signature to your outgoing emails, allowing the receiving server to verify that the email was indeed sent by your domain and that its content hasn't been altered in transit.
DMARC: Domain-based Message Authentication, Reporting, and Conformance builds on SPF and DKIM, telling receiving servers what to do if an email fails authentication (e.g., p=quarantine, p=reject) and provides reporting on email authentication failures.
Implementing DMARC with a policy of p=reject or p=quarantine is critical for strong domain protection and deliverability. If you're using an Email Service Provider (ESP), ensure your SPF, DKIM, and DMARC records are correctly configured for your sending domain, ideally with your ESP's guidance. This step is fundamental to boosting email deliverability rates and avoiding potential blocklists (or blacklists). You can learn more about these protocols in this simple guide to DMARC, SPF, and DKIM.
Setting up these authentication records correctly is not just a technical formality, it's a critical signal to corporate email systems that your emails are legitimate and trustworthy. Failing to do so can lead to immediate rejections or misdirection to spam folders, regardless of your content or list quality.
Optimize content and engagement to avoid spam traps
Even with perfect technical setup, your content and how recipients interact with it significantly influence deliverability. B2B recipients, particularly within large organizations, have sophisticated spam filters that scrutinize email content for common spam triggers and low engagement signals. If your nurturing emails aren't opened, clicked, or are frequently deleted without engagement, this negatively impacts your sender reputation.
Common pitfalls
Generic subject lines: Phrases like 'Important update' without personalization or clear value proposition can trigger spam filters.
Heavy images or code: Emails that are mostly images with little text can look suspicious to filters. Avoid JavaScript or Flash in email design.
Infrequent or inconsistent sending: Sending emails erratically can raise red flags with mailbox providers, impacting trust.
Irrelevant content: Sending product updates to customers who signed up for a specific service can lead to disengagement and spam complaints.
Best practices
Personalization: Use the recipient's name or company name in the subject line and body. Tailor content to their specific needs or product usage.
Clear sender name: Use a recognizable sender name, like a person's name from your team or your company name, to build trust.
Consistent sending cadence: Send emails at a predictable frequency. This helps subscribers know what to expect and can improve engagement.
Compelling subject lines: Craft subject lines that are concise, descriptive, and create curiosity without being clickbait-y. Avoid spam trigger words.
Furthermore, be mindful of spam traps. These are email addresses used by ISPs to identify senders who are not following best practices, typically by sending to old or unengaged lists. Hitting spam traps indicates poor list hygiene and can severely damage your sender reputation, leading to blocklisting (or blacklisting).
Focus on creating valuable, relevant content for your B2B customers. Ensure your emails are easy to read and provide clear calls to action. A high-quality email that generates engagement is far less likely to be marked as spam. For more ideas on how to improve open rates, check out this guide on how to increase email click through rate. A complete guide to improving email deliverability by Allegrow also provides extensive insights.
Maintain a clean and engaged email list
Even for nurturing existing customers, list quality is critical. Over time, email addresses become inactive, companies change domains, or employees leave. Sending to old or unengaged addresses increases your bounce rate and can lead to spam complaints, particularly if recipients no longer recognize your brand or email type.
Implement a rigorous list hygiene strategy. This includes regularly removing hard bounces and soft bounces that consistently fail after several attempts. Additionally, identify and segment inactive subscribers. While these are customers, if they haven't opened or clicked your nurturing emails in a long time, consider sending them re-engagement campaigns. If they still don't respond, it might be better to remove them from your active nurturing list to protect your sender reputation.
Honoring unsubscribe requests
Always, and I mean always, honor unsubscribe requests immediately. Sending emails to recipients who have opted out is a surefire way to get marked as spam, accumulate complaints, and potentially end up on a blocklist (or blacklist). Even if your emails are technically transactional, if they are perceived as marketing or nurturing by the recipient and they’ve opted out, continuing to send can cause severe deliverability issues. This also aligns with new guidelines from Yahoo and Google around one-click unsubscribe. Regularly review your unsubscribe process to ensure it's seamless and effective.
Consider implementing double opt-in for new sign-ups, even for customer communications. While your existing customers have a relationship with you, this can help verify active addresses and reduce the risk of future bounces. For comprehensive strategies, review effective approaches to avoid spam traps and improve deliverability.
Views from the trenches
Best practices
Regularly clean your email lists by removing invalid or unengaged subscribers to prevent bounces and maintain a good sender reputation.
Segment your audience and send highly relevant, personalized content to increase engagement and reduce spam complaints.
Gradually warm up new sending domains or IPs by starting with small volumes to highly engaged users and slowly scaling up.
Always honor unsubscribe requests immediately and ensure your unsubscribe process is easy for recipients to find and use.
Implement SPF, DKIM, and DMARC protocols correctly to authenticate your emails and build trust with mailbox providers.
Common pitfalls
Sending emails to recipients who have not opted in, which can lead to high spam complaint rates and blocklisting.
Using generic subject lines or email content that triggers spam filters and reduces open rates.
Ignoring bounce rates and not removing inactive email addresses, which damages sender reputation over time.
Inconsistent sending volume or frequency, which can appear suspicious to ISPs and lead to throttling or blocking.
Not monitoring email deliverability performance, leaving issues unaddressed until they significantly impact campaigns.
Expert tips
Actively monitor your sending domain's reputation using tools like Google Postmaster Tools to identify issues early.
Understand the difference between transactional and nurturing emails; ensure your messaging aligns with how recipients perceive it and how opt-outs are handled.
Consider the specific spam filtering challenges posed by B2B corporate networks, which are often more aggressive than consumer-facing ISPs.
Review your ESP's anti-spam policy to ensure your sending practices align with their guidelines.
Focus on delivering consistent value in your nurturing content to encourage engagement and positive interactions from customers.
Marketer view
Marketer from Email Geeks says that if people are not opting in to receive your mail, you're going to need significant help to improve deliverability, as consent is fundamental.
2022-02-07 - Email Geeks
Marketer view
Marketer from Email Geeks mentioned that they send nurture campaigns, product announcements, and welcome emails, all of which include opt-outs. They found their deliverability stats were good, but open rates were low, indicating emails weren't reaching inboxes, despite honoring unsubscribes.
2022-02-07 - Email Geeks
Final thoughts on B2B email deliverability
Improving B2B email deliverability for customer nurturing is a continuous process that combines technical diligence with strategic content and list management. It requires understanding the nuances of corporate spam filters and consistently demonstrating to mailbox providers that you are a responsible and valuable sender.
By focusing on a strong sender reputation, implementing proper email authentication (SPF, DKIM, DMARC), crafting engaging and relevant content, and maintaining a clean list, you can significantly increase the chances of your nurturing emails reaching your customers' inboxes. Remember that even small block rates can indicate underlying issues that need attention.
Don't underestimate the power of consistent monitoring and adaptation. Regularly check your deliverability metrics, respond to feedback loops, and adjust your strategy based on performance. This proactive approach will help you overcome the challenges of B2B email deliverability and ensure your nurturing efforts yield the best possible results.
