Cold Email Deliverability: The Foundation of Success in 2025

Cold emailing remains one of the most powerful tools for building a sales pipeline, yet the landscape is evolving rapidly. Whether you're a growth marketer, SaaS company, agency, or GTM engineer, mastering cold email deliverability and response optimisation is essential to success. In this comprehensive article, we dive deep into the future of cold emailing, drawing insights from industry experts Frank from Salesforge and Jeremy from QuickMail. Their combined experience and data-driven approach shed light on how to avoid spam filters, scale your outreach, and leverage technological innovations to maximise reply rates and pipeline growth.

Introduction to Cold Emailing Today

Cold emailing is no longer just about firing off mass emails and hoping for replies. It’s a complex ecosystem involving email service providers (ESPs), infrastructure setup, deliverability protocols, recipient behaviour, and continuous optimisation. Frank and Jeremy bring decades of combined experience - from building cold email automation software to running large sales teams scaling millions in revenue - to offer actionable insights into the present and future of cold email outreach.

They emphasise that cold emailing is just one pillar of a multi-channel outreach strategy that includes LinkedIn and cold calling. However, this discussion focuses purely on cold email, exploring how to get your emails delivered, opened, and replied to in 2025 and beyond.

Understanding the Cold Email Ecosystem

At the core of successful cold emailing lies four pillars:

1. Execution: How and when you send emails, managing sequences, pacing, and tracking.
2. Infrastructure: The technical setup behind your email domains, IPs, and sending platforms.
3. Copy: Crafting compelling, relevant messages that engage your audience.
4. Leads: Targeting the right prospects with clean, verified, and relevant data.

Frank and Jeremy focus heavily on the infrastructure and execution aspects, providing deep insights into deliverability, domain management, sender reputation, and how AI and automation are shaping the future.

Cold Email Deliverability: The Technical Backbone

Key Deliverability Factors

Deliverability is primarily influenced by your technical setup. Essential components include:

• SPF, DKIM, and DMARC: Authentication protocols that verify your emails are legitimate and not spoofed.
• Email Service Providers (ESPs): The platform or provider you use to send emails (Google Workspace, Microsoft 365, SMTP providers, etc.)
• IP Reputation: The standing of the IP addresses sending your emails, whether shared or dedicated.
• Domain Reputation: The trustworthiness of your sending domain, which can be affected by spam complaints and blacklisting.
• Warm-up Processes: Gradually increasing sending volumes and engagement to build a positive reputation.

Jeremy highlights that deliverability is a complex, ongoing process - it’s not a one-time setup. He recommends using multiple ESPs and domains to diversify sending sources and mitigate risks.

ESP-Specific Trends and Challenges

Data from millions of emails sent through QuickMail reveals interesting trends:

• Gmail: Currently experiencing a decline in reply rates, possibly due to increased spam filters and user behaviour changes. Google’s spam policies and banner warnings (like the “show images” prompt) can negatively impact engagement.
• Microsoft Outlook: More stable with consistent reply rates, but generally lower than Gmail. Outlook seems less affected by recent changes and does not display the same intrusive banners.
• SMTP Providers: Highly variable results depending on the reputation of the IPs and the SMTP server configurations. Shared IP pools can be cost-effective but riskier in terms of reputation, while dedicated IPs provide control but require expertise to manage.

Frank advises that for most B2B cold emailing, Google Workspace and Microsoft 365 remain the safest bets. Diversifying across two to four ESPs is optimal, with Gmail and Outlook being the primary drivers.

Innovations Shaping the Future of Cold Emailing

Deliverability AI and Inbox Rotation

QuickMail has pioneered two key innovations:

• Inbox Rotation: Automatically balances sending volume across multiple email addresses, keeping individual inboxes under spam radar thresholds.
• Deliverability AI: Monitors daily inbox performance and dynamically swaps underperforming email accounts with healthier ones to maintain high deliverability.

These technologies allow users to manage up to 200 email accounts seamlessly, maximising outreach capacity while minimising the risk of being flagged as spam. Such automation is poised to be a game changer in 2025.

AI-Powered Copy Variation

Traditional cold emailing often relies on spintax - complex, hard-to-maintain templates for creating variations of emails to avoid spam filters. QuickMail replaces this with AI that rephrases emails while preserving meaning. This approach enables more natural, readable messages and enables meaningful A/B testing of different ideas and unique selling points.

Data-Driven Insights: What the Numbers Tell Us

Reply Rates Over Time

Analyzing aggregated data from millions of emails, Frank and Jeremy observed:

• A significant drop in reply rates around May-June 2023, coinciding with updates to spam filters by Google and Microsoft.
• Gmail’s reply rates have declined, while Outlook’s remained relatively stable.
• Reply rates vary substantially depending on the combination of sender and recipient ESPs (e.g., Gmail-to-Gmail performs differently than Gmail-to-Outlook).

These insights emphasise the dynamic nature of cold email deliverability and the importance of continuous monitoring and adaptation.

ESP Matching Myth Debunked

Contrary to popular belief, sending emails from the same ESP as your recipient (ESP matching) does not necessarily improve reply rates. Data shows that Outlook recipients are indifferent to sender ESP, while Gmail recipients tend to penalise same-ESP senders more strictly due to their access to comprehensive user behaviour data.

Open Tracking: Friend or Foe?

Open tracking uses invisible pixels to detect when an email is opened. While marketers love this metric, Frank and Jeremy caution against relying on it for cold emails.

• Open tracking can hurt deliverability: Gmail’s “show images” banner introduced in 2023 has increased spam complaints among recipients who see suspicious tracking attempts.
• Open rates are unreliable: Different ESPs handle pixel tracking differently, causing open rates to vary by up to 20 percentage points between providers like Google and Microsoft.
• Reply rates matter more: Jeremy recommends focusing on reply rates, unsubscribe rates, and spam complaints as more reliable indicators of campaign health.

Interestingly, data shows campaigns with open tracking turned off enjoy more than double the reply rates compared to those with tracking enabled. Frank recommends disabling open tracking by default or enabling it only on follow-up emails as a diagnostic tool.

Building a Robust Cold Email Infrastructure

Choosing Domains and Mailboxes

Domain reputation is crucial for deliverability. Key recommendations include:

• Use .com domains: These are more trusted by recipients and less likely to be flagged as spam compared to newer or uncommon TLDs like .net, .co, or .ai.
• Buy localized domains: For targeting specific markets, use country-code TLDs such as .co.uk for the UK, .fr for France, and .de for Germany to increase trust and relevance.
• Set up multiple mailboxes per domain: Professionals typically create 2 mailboxes per domain to distribute sending volume and reduce risk.
• Limit sending volume per mailbox: Aim for no more than 30 cold emails per mailbox per day, with some sending as few as 5 to 10 depending on context.

Frank notes that domains tend to “burn” after 4-6 months, necessitating a strategy of buying batches of domains and rotating them proactively to maintain deliverability.

Shared vs Dedicated IPs

There is no one-size-fits-all answer when choosing between shared and dedicated IPs:

• Shared IP pools: Cost-effective and easier to set up but risk being affected by other users’ behaviour.
• Dedicated IPs: Offer control over your sender reputation but require expert management and investment in warm-up processes.

For new senders, shared IPs often make more sense, whereas experienced senders with strict best practices may benefit from dedicated IPs.

Warm-Up Pools: The Controversy and Best Practices

Warm-up pools are automated systems that send and receive emails to build sender reputation gradually. While popular, they are not without controversy:

• Google actively discourages warm-up pools: They may send warnings if suspicious activity is detected.
• Quality matters: Warm-up pools must consist of “good” domains and avoid sensitive categories like gambling to prevent reputation damage.
• Composition is key: If your target audience is primarily Gmail, your warm-up pool must include Gmail accounts to be effective.
• Bounce rates during warm-up should be near zero: High bounce rates indicate poor quality lists or misconfigured pools.

Warm-up pools do work but require due diligence, quality control, and ongoing monitoring to be effective.

Execution Strategies for Maximum Engagement

Sequencing and Pacing

Effective cold email sequences balance frequency with recipient tolerance:

• Limit sequence length: Most pros send 2-3 emails per sequence to reduce spam complaints.
• Space out emails: Sending one email per week or spacing follow-ups by 3-7 days helps avoid overwhelming recipients.
• Repeat quarterly: Since only 2-3% of prospects are typically in-market at any time, repeat outreach 3-4 times per year with updated messaging.

Frank notes that spam complaints tend to increase significantly after the second email in a sequence, so keeping sequences short and respectful is critical.

Copywriting and Engagement

Copy remains king in cold email success. Key tips include:

• Use strong, relevant CTAs: Clear calls to action that align with the prospect’s pain points.
• Inject personality and humour: Using a funny or clever P.S. can prompt replies even from uninterested recipients.
• Personalise and target: Avoid generic, database-scraped lists. Use lookalike data or carefully curated lists for better engagement.
• Avoid spammy language: Poorly written or irrelevant emails increase spam complaints and hurt deliverability.

Jeremy shares an example of a playful P.S. encouraging recipients to “tell me to unsubscribe and tell me to f*** off,” which can prompt responses and improve engagement metrics.

Targeting and Lead Quality

Lead quality dramatically impacts cold email success:

• Clean your lists: Use email verification tools to reduce bounce rates.
• Understand your ICP: Know the typical ESPs your prospects use and tailor infrastructure accordingly.
• Avoid oversaturated data: Large databases like Apollo or ZoomInfo sell the same contacts to multiple companies, increasing competition and reducing reply rates.
• Seek exclusive or hard-to-find leads: These are less likely to be spammed and more likely to engage.

Cold Emailing to Enterprise and Fortune 500 Companies

Reaching high-security enterprise inboxes is notoriously difficult. Frank advises:

• Avoid dedicated IPs: Enterprise email security tools like Proofpoint or Mimecast share blacklists across networks, blocking emails from dedicated IPs quickly.
• Use shared IP pools: This dilutes sender reputation and reduces the risk of being blocked across entire enterprise networks.
• Focus on Google Workspace and Microsoft 365: These platforms dominate enterprise email and provide the best chance of landing in primary inboxes.

Maintaining and Scaling Your Cold Email Program

Cold email infrastructure and campaigns require ongoing maintenance:

• Run regular placement tests: Use seed lists to verify whether emails land in primary inboxes or spam folders across multiple ESPs.
• Monitor domain and IP health: Check blacklists, bounce rates, and spam complaints frequently.
• Rotate domains and mailboxes: Replace burned infrastructure proactively every 4-6 months.
• Continuously optimise copy and targeting: Refresh messaging quarterly to reflect market changes and maintain engagement.

Frank and Jeremy stress that cold emailing is a marathon, not a sprint. Success comes from disciplined execution, data-driven adjustments, and smart use of technology.

Where to Go From Here

Both experts encourage cold email practitioners to leverage the latest tools and data to stay ahead. Frank recommends connecting on LinkedIn for personalised advice, while Jeremy advocates signing up for the QuickMail newsletter for exclusive insights.

Emerging AI-driven features like deliverability monitoring, inbox rotation, and AI-powered copywriting will continue to reshape cold emailing in 2025 and beyond. The key takeaway is to prioritise deliverability and engagement over vanity metrics like open rates, invest in clean infrastructure, and maintain respectful, relevant outreach.

Conclusion

Cold emailing is evolving into a sophisticated, data-driven discipline where technical infrastructure, sender reputation, and recipient behaviour intersect. The future belongs to those who embrace AI-powered automation, diversify their sending infrastructure, and focus relentlessly on building genuine engagement.

By following the best practices outlined by Frank from Salesforge and Jeremy from QuickMail - ranging from domain management and warm-up strategies to copywriting and lead targeting - you can maximise your cold email reply rates and build a robust sales pipeline in 2025.

Remember, cold email success is not just about volume but about quality, consistency, and adaptability. Stay informed, test regularly, and never stop optimising.