[Last Update: December 2024]
How long did it take to create this Guide? About 15 years. Delivering cold emails to inboxes demands extensive experience—years of testing, strategy development, evolving tactics, and countless campaigns. Mastering cold email marketing requires deep knowledge of bulk emailing, sending servers, IPs, SMTP, industry players, and spam algorithms. We’re excited to share our insights, tips, and strategies with you. Enjoy!
Recommended Tools
Cold Email, Rotating System with Full CRM Functionalities and Unlimited Storage
Table of content
- 1. How does cold email deliverability sender reputation work?
- 2. How can email deliverability be REALLY improved?
- 3. What are the best email deliverability practices to follow?
- 4. What is the best service to use when sending cold bulk emails?
- 5. How can I send 10K cold emails per day?
- 6. How to check an email delivery campaign’s reputation?
- 7. What is the difference between email soft bounce and hard bounce?
- 8. Which is the best tool to check email deliverability score?
- 9. Is there a way to boost email reputation?
- 10. What do you mean by email deliverability service, and what are the advantages of B2B email deliverability services?
- 11. What does it mean when your email has low deliverability?
- 12. What are the benefits of Email Deliverability services?
- 13. Does linking my website in a cold email look like spam?
- 14. Given the effectiveness of spam filters, is cold emailing 'over'?
- 15. Is cold email spam?
- 16. What is the best service to use when sending cold bulk emails, and what is the best platform to send cold emails from?
- 17. How can I detect spam traps among my user list?
- 18. What is the best tool for cold email marketing?
- 19. How can email deliverability be improved, and How to deal with email deliverability issues?
- 20. What is a dedicated IP in email marketing?
- 21. Do I need a shared IP or a dedicated IP for my email marketing?
- 22. In email marketing, what is an IP warm-up?
What is The Main Challenge in Cold Emailing?
The primary challenge with cold email campaigns is deliverability—your ability to consistently land emails in recipients’ inboxes while avoiding spam filters. Strong deliverability directly correlates with your success in reaching new audiences through cold emails.
Understanding Spam Filters
To maximize deliverability, it’s essential to grasp how spam filters work and how to validate your sending infrastructure. Internet Service Providers (ISPs) deploy advanced algorithms to identify bot-like behavior and flag suspicious activity. Emails flagged as suspicious are either diverted to spam folders or blocked outright.
One of the most common triggers is sending large volumes of emails from a new or unverified IP address. ISPs see this as a potential spammer activity. To avoid being flagged, you must build a strong sender reputation with ISPs. This involves establishing trust over time by mimicking natural, human-like email behavior.
This reputation-building process is often referred to as email validation and is critical to ensuring that your cold emails reach their intended recipients. It’s not just about what you send—it’s about how you send it. Strategies like email warm-ups, compliance with protocols like SPF and DMARC, and careful monitoring of engagement rates all play a role in appearing trustworthy to ISPs.
How Does Sender Reputation Affect Cold Email Deliverability?
Cold email deliverability is the measure of how successfully your email campaigns reach recipients’ inboxes rather than being flagged as spam. A critical factor influencing deliverability is sender reputation, a score assigned by each mailbox provider or ISP (such as Gmail, Yahoo, or Hotmail).
Sender reputation reflects the trustworthiness of your emails in the eyes of these providers. This trust is shaped by several factors, including:
Your IP’s Campaign History: A consistent track record of legitimate, non-spam activity builds credibility.
Domain Reputation: The domain you use to send emails must be properly authenticated and associated with trustworthy activity.
URLs in Your Emails: Links should be valid, relevant, and free of redirects or blacklisted sites.
Content Quality: ISPs analyze the structure, language, and formatting of your emails to detect spam-like patterns.
Maintaining a high sender reputation requires a strategic approach to campaign management, ensuring alignment with best practices for email content, compliance, and technical setups like SPF, DKIM, and DMARC protocols.
How Can Email Deliverability Be Truly Improved?
Improving email deliverability starts with enhancing the reputation of the server or IP used to send your emails. However, for those in the cold email business, even the best practices can’t entirely prevent challenges. Cold email campaigns inherently face risks: recipients who didn’t request your emails may flag them as spam, potentially impacting your sender reputation.
Here’s an overview of common approaches to sending cold emails and why they often fall short when scaled:
Conventional Email Platforms with Shared IPs
Many start their cold email journey using platforms like ActiveCampaign, Brevo, MailerLite, or ConvertKit. These platforms typically rely on shared IPs, which are managed to maintain a strong reputation across their user base.
Why It Fails for Cold Emails:
These platforms are not built for cold email campaigns. If they detect bulk uploads of contact lists, low open rates, or high complaint rates, they will flag your activity and suspend your account. Their priority is maintaining their shared IP reputation, which means cold emailers are seen as a liability, regardless of their intentions. The high costs associated with these platforms also make them impractical for long-term cold outreach.
Dedicated IPs and Servers
After shared IPs prove unsuitable, many turn to dedicated IPs or private servers via providers like Postmark, Brevo’s dedicated services, or hosting platforms such as Contabo and DigitalOcean.
Why It Fails for Cold Emails:
Dedicated IPs require significant investment in proper warm-ups, a gradual process of sending small volumes of emails to build trust with ISPs. If your campaigns generate hard bounces, spam complaints, or low engagement, your dedicated IP will be flagged or blacklisted. Worse, providers like Postmark or Contabo will suspend your account at the first sign of issues, leaving you with wasted resources and no recourse.
Systems with External Mailboxes
Some marketers opt for systems that integrate with multiple external mailboxes, such as SMTP services, cloud-based email servers, or third-party providers like Google Workspace or Outlook 365. This approach offers greater flexibility by decentralizing the sending process, reducing dependence on a single platform’s IP reputation.
Why It Faces Challenges:
Managing multiple mailboxes requires robust oversight. Every mailbox must have proper email authentication protocols (SPF, DKIM, DMARC) in place to maintain deliverability. Additionally, if one mailbox experiences complaints or is flagged, it can drag down the performance of your entire campaign. Without rigorous monitoring and a scalable infrastructure, the risks remain high.
The Key Takeaway
Cold email campaigns require more than just switching between platforms or providers. To achieve sustainable deliverability, you need a customized system designed for flexibility, compliance, and ongoing reputation management. This includes:
Properly warming up new domains and IPs.
Regularly validating email lists to minimize bounces.
Diversifying your sending infrastructure to reduce dependency on any single provider.
Maintaining consistent engagement and avoiding spam triggers.
Cold email success lies not in the tools themselves but in how strategically they’re set up and managed. A well-structured approach ensures that your emails don’t just get sent—they get delivered.
Then what are the best email deliverability practices to follow?
1. Rotating Senders (Domains and IPs)
To avoid overloading any single domain or IP and risking flagging by ISPs, we rotate between multiple sending domains and IP addresses. This tactic ensures a distributed email load, reducing the chances of reputation damage.
Trend Insight: According to MarTech News, the use of multiple domains is becoming standard among high-volume email marketers, particularly for cold outreach. However, ISPs are now monitoring domain clusters, making proper diversification essential.
2. Diversifying Providers
We send emails from a mix of mailboxes, including Google Workspace, Outlook, Mailgun, and VPS providers. This diversification mitigates the risk of account suspension or delivery blocks from any one provider.
Supporting Data: Research from Email Vendor Selection highlights that campaigns spread across platforms experience a 23% lower rate of account suspension compared to those relying on a single provider.
3. Warming Up SMTP Servers
Before ramping up email volume, we warm up SMTP servers for at least two weeks to build sender trust gradually. During this period, emails are sent in small batches, engaging recipients to establish a reputation for legitimate activity.
Case Study: A campaign we ran for a tech startup saw a 30% increase in open rates after a proper warm-up process, compared to rushed deployments that led to high spam complaints.
4. Using Plain Text for Initial Emails
We start every campaign with plain-text emails—no links, no images. This lowers spam scores and increases the likelihood of hitting the inbox, establishing a foundation of engagement before scaling up content-rich emails.
Recent Trend: Fast Company reports that minimalistic emails, especially in cold outreach, are outperforming HTML-heavy formats, with open rates up by 15% on average.
5. Leveraging Email Warming Systems
Email warming systems like Warmbox or Lemwarm help pre-engage with mail servers, moving emails from spam to primary inboxes. These systems not only boost deliverability but also provide valuable insights into how ISPs perceive your campaigns.
Industry Growth: The email warming market is expected to grow by 12% annually, reflecting its critical role in email marketing infrastructure.
6. Real-Time Bounce Management
Hard bounces harm sender reputation. We remove invalid emails immediately upon detection, keeping our lists clean and ensuring ISPs see our campaigns as legitimate.
Supporting Data: According to Litmus, hard bounces account for 6-10% of emails in poorly maintained lists, but regular hygiene reduces this to under 1%.
7. Email Authentication (SPF, DKIM, DMARC)
Proper email authentication protocols, like SPF, DKIM, and DMARC, are essential for proving legitimacy and preventing spoofing. ISPs rely heavily on these standards to evaluate trustworthiness.
Fact: Hornetsecurity states that 78% of phishing attacks exploit poor or absent email authentication, making this a non-negotiable for cold email campaigns.
8. Monitoring Engagement Metrics
Tracking open rates, clicks, and replies allows us to focus on engaged recipients while removing non-responsive contacts. This ensures campaigns remain relevant and boosts sender reputation.
Trend Insight: AI-driven engagement monitoring tools are on the rise, enabling real-time adjustments that optimize ongoing campaigns.
9. Personalizing Emails at Scale
ISPs reward relevance. Personalization—such as referencing the recipient’s name, company, or industry-specific pain points—signals to algorithms that emails are wanted.
Case Study: A recruitment campaign we managed showed a 40% higher reply rate when personalization was added to subject lines and opening sentences.
10. Regular List Cleaning
Regular list verification ensures your campaigns target valid, engaged contacts. Removing inactive or unverified addresses reduces bounce rates and flags from ISPs.
Supporting Data: Email lists that are cleaned quarterly see a 25% improvement in deliverability, according to a report by Email Marketing Insights.
The Future of Deliverability Practices
As we approach 2025, cold email strategies are becoming more nuanced. With data privacy laws like GDPR and CCPA shaping compliance standards, marketers will need to adopt tools that ensure both legality and efficiency. AI-powered tools are also emerging as game-changers for email warming, list verification, and real-time engagement tracking.
Copywriting/Content Strategy
The Real Secret to Effective Subject Lines in Cold Emails
Based on our experience running thousands of successful cold email campaigns across industries, the key to crafting a subject line that drives opens isn’t just personalization—it’s relevant, specific insight that makes the recipient feel seen and valued. Here’s what we’ve learned:
Go Beyond the Basics
Mentioning their company name or location in the subject line is no longer enough. Marketers have been using this tactic for years, and recipients recognize it immediately as templated. To stand out, you need to reference something unique about them—something tied directly to their work, achievements, or online presence.Example for Influencers:
If you’re targeting Instagram influencers, highlight their hard-earned follower count:
Subject Line: “[InfluencerHandle]—150,000 followers and growing! Here’s why I reached out.”
Why it works: Influencers work tirelessly to build their audience. Mentioning this shows you’ve noticed and respect their effort, making them more likely to engage.
Make It About Their Work
Whether it’s a pest control company, retailer, or service provider, referencing their work—especially something they’re proud of—grabs attention.Example for Pest Control Companies:
Highlight a customer review from their website or Google My Business profile:Subject Line: “I saw Stephanie McCain’s review—this is why I’m reaching out.”
Why it works: Reviews are often personal and meaningful to businesses. Calling one out shows you’ve done your homework and aren’t just sending mass emails.
Example for Retailers:
Go deeper than their location. Reference a unique aspect of their offerings or a product they’re promoting:Subject Line: “Spotted your latest spring collection—let’s talk about boosting it.”
Why it works: Specificity signals effort and interest, increasing the likelihood of engagement.
Use Words That Work
Certain words and phrases consistently perform better, but only when used naturally within a subject line. Words like “new,” “most,” and “read” draw attention, especially when used strategically.Example:
Subject Line: “New ways to double [Your Company’s Service ROI].”
Subject Line: “Read this before your next product launch.”
Why it works: These words imply value and urgency, making recipients curious without feeling pressured.
Personalization That Feels Earned
Including their first name is standard and often ignored. Instead, focus on something that feels like you’ve earned the right to their attention by researching who they are and what they’ve done.What Doesn’t Work:
“Hi [First Name], I wanted to reach out.”
Why: It’s generic and shows no real effort.
What Works:
“Hi [First Name], saw your article on [Topic]—here’s why I’m reaching out.”
Why: This approach feels thoughtful and authentic, opening the door to further engagement.
Demonstrate You Understand Their Goals
Your subject line should reflect that you understand what they’re striving for and have something valuable to offer.Example for Tech Companies:
Subject Line: “Your SaaS scaling journey—let’s talk growth solutions.”
Why it works: It ties your outreach directly to their likely pain points or ambitions.
Takeaway: Effort = Engagement
Cold emails succeed when the recipient feels the sender has invested real effort in understanding their needs and goals. Your subject line should reflect that effort by incorporating specific, relevant insights about their business, work, or achievements.
Anything less is just another email in their crowded inbox—and no one opens those.
Example:
Recently, we sent cold emails for a client targeting over 100,000 Instagram influencers in a specific niche.
Our strategy included adding each influencer’s follower count to the subject line. For instance, we used, “@… 56,644 followers and counting!”
This simple tweak made the subject line highly personalized and relevant, leading to an open rate that went through the roof.
What is the best service to use when sending cold bulk emails?
The Best Service for Bulk Cold Emails and Outreach: Why Omnily.io Stands Out
When it comes to email marketing, platforms like ActiveCampaign, Brevo, and MailerLite are excellent for managing existing subscribers. However, they are not suitable for cold bulk emailing. These platforms rely on shared IPs with strong reputations, which they protect rigorously. If they detect cold emailing activities—low engagement rates, high bounce rates, or spam complaints—they will suspend your account to safeguard their IP deliverability.
This makes traditional email marketing tools ill-suited for cold outreach, as they are optimized for nurturing opt-in subscribers rather than reaching out to new prospects.
Why Conventional Cold Email Tools Fall Short
Cold email-specific tools like Apollo, Woodpecker, Saleshandy, Hunter.io, and Instantly are designed to support cold outreach. They allow you to manage multiple mailboxes, send personalized cold emails at scale, and connect with large email lists.
While these tools excel in initial outreach, they often lack the depth required for fully integrated sales and marketing processes:
Limited Drip Campaigns: These tools don’t offer advanced workflows with conditional logic, tagging, or event-based actions. For example, automatically moving prospects from a cold drip to a nurture sequence after a reply often requires manual intervention or unreliable external integrations.
Weak CRM Integration: Cold email is just the first step in the sales funnel. Transitioning engaged prospects into a CRM or marketing platform for further nurturing (via SMS, calls, and advanced tracking) often requires integrations through Zapier or similar services, which can be unreliable and insufficient.
Why Omnily.io Is the Ultimate Cold Outreach and CRM Platform
Omnily.io offers a comprehensive solution for cold email campaigns and beyond, seamlessly blending appointment-setting capabilities, cold outreach features, and a full-fledged CRM. Here’s why Omnily.io stands out as the go-to platform for scaling your business outreach efforts:
1. Advanced Email Infrastructure
Rotating IPs and Mailboxes: Automatically rotate sending domains and mailboxes to distribute the email load and maintain healthy reputations across servers.
Unlimited Sending Domains: Connect and manage as many domains as needed for diverse and reputable campaigns.
Dynamic Domain Rotation: With up to 100 domains (or more), Omnily.io ensures no single domain exceeds its quota, keeping your deliverability high.
In-System Address Verification: Clean email lists with built-in email verification, reducing hard bounces and protecting sender reputation.
2. Cutting-Edge Drip Campaign Features
Conditional Logic and Automation: Create advanced workflows that adapt based on recipient engagement. For example, move a prospect to a sales follow-up sequence automatically after they reply.
Tagging and Event-Based Triggers: Use tags and triggers to personalize workflows further, ensuring tailored communication at every step.
Scalable Campaigns: Send unlimited emails with no restrictions on volume or data, allowing you to grow your outreach efforts without limits.
3. Fully Integrated CRM Functionality
Unlike standalone cold email tools, Omnily.io is also a robust CRM, offering features that include:
Contact Management: Organize leads, track interactions, and prioritize follow-ups effortlessly.
Task Automation: Automate reminders, tasks, and updates to ensure no lead falls through the cracks.
SMS and Call Integration: Communicate through multiple channels directly from the platform, complementing your email outreach.
Sales Opportunity Tracking: Track prospects throughout the sales funnel, from initial contact to closing deals.
Comprehensive Reporting: Get detailed insights into campaign performance, sales metrics, and pipeline health.
4. Streamlined Setup and Onboarding
Direct Domain Acquisition: Omnily.io allows you to purchase and configure domains directly within the platform, reducing the time and complexity of external setups.
End-to-End Sales Management: Manage every aspect of the sales process, from outreach to closing, without needing external tools or integrations.
Why Omnily.io Is Ideal for Cold Email and Beyond
With Omnily.io, you don’t just get a cold email platform—you get an integrated system for scaling your outreach and managing your sales funnel seamlessly. By combining the technical infrastructure for email deliverability with powerful CRM capabilities, Omnily.io is the ultimate solution for businesses looking to scale efficiently and effectively.
For industries ranging from SaaS and real estate to professional services and B2B tech, Omnily.io delivers a scalable, compliant, and results-driven platform. If you’re serious about cold outreach and sales, this is the tool that will help you dominate in 2025 and beyond.
How can I send 10K cold emails per day?
We recommend the following practice to get the best deliverability when sending 10K cold emails per day:
* 4-5 rotating IPs
* 3 Rotating sending domains
* Warm up your servers, diversify your mailbox providers, and plan your campaigns to ensure that no sender sends an excessive amount of emails in a way that could trigger spam flags.
How to Check an Email Delivery Campaign’s Reputation?
Check Hard Bounce Rates
An email bounces when the ISP (e.g., Gmail, Yahoo, etc.) or the server returns the email without delivering it. A hard bounce usually occurs when the address is incorrect or there is another permanent issue with the address. Hard bounces harm your sender reputation, so you should avoid them by verifying all addresses before emailing them.Check Complaint Rates
Monitor the number of complaints your campaign receives, as high complaint rates can negatively impact your sender reputation.Check Your Opening Performance and Campaign Stats Regularly
If your open rate is sufficient, your emails are likely reaching the inbox rather than the spam folder, which is great news. However, if your click rate is low, it means people are opening your emails but not engaging further. This could indicate that your content needs improvement, or that your messages should be more segmented and relevant.
If there are no bounces or spam reports but open rates are low, your subject line might not be strong enough, or your content might not resonate with your audience. Understand your audience, learn what they need, and use your emails to communicate with them on a level that is valuable to them.Send Tests to Multiple Email Addresses and Check the Delivery Tabs
Send test emails to multiple addresses to see where they land—in the primary inbox, promotions, or spam folder. This will help you adjust your content and sending strategy to improve deliverability.
What is the difference between an email soft bounce and a hard bounce?
A soft bounce occurs when an email reaches the destination server but is not delivered to the recipient’s inbox, often because the inbox is full, temporarily unavailable, or inactive. Soft bounces do not significantly harm your sender reputation.
Hard bounces, on the other hand, are detrimental to your sender reputation. They indicate a permanent error, such as an incorrect or non-existent address, preventing the email from being delivered. To avoid hard bounces, ensure you clean and verify your email lists before sending cold campaigns.
Which is the best tool to check email deliverability score?
ZeroBounce Score™ is a tool that uses artificial intelligence to assess how your subscribers may interact with your cold emails. By detecting email activity levels, the tool can indicate how likely you are to reach a real person on the other end of an email. The scores range from 0 to 10, with 10 being the highest quality rating.
Is there a way to boost email reputation?
The strategy that the team at Omni Online Strategies has developed to boost email reputation consists of:
3 Main IPs that are kept clean, active, and validated. These IPs are used to send emails to your best contacts—those who consistently engage and trust your messages.
28 Warm-Up IPs used to send initial emails, identify bounces, and remove unengaging contacts. The purpose of these IPs is to filter and identify the most responsive contacts in your lists. Once identified, these high-quality contacts are moved to the Main IPs for continued communication. The aim is to keep these Main IPs healthy and maintain a high sender reputation. While the warm-up IPs may eventually get burned and go out of use, by that time, you should have built a clean, verified, and segmented list of engaged recipients who know you, trust your emails, and respond to your messages.
Deep Segmentation of contact lists allows for personalized, valuable communication, leading to higher engagement and improved sender reputation.
