How to Set Up Custom Domains for Cold Email

Want your cold emails to land in inboxes, not spam folders? Setting up custom domains is the key. It protects your main domain, improves deliverability, and ensures compliance with email laws. Here's a quick breakdown of how to do it:

• Why Use Custom Domains?
  • Shields your primary domain from blacklisting.
  • Improves email deliverability with proper authentication (SPF, DKIM, DMARC).
  • Helps comply with laws like the CAN-SPAM Act (penalties up to $53,088 per email).
• Steps to Get Started:
  1. Choose a Domain: Use a variation of your main domain (e.g., yourcompany.net or yourcompany.io) for branding and protection.
  2. Register the Domain: Costs range from $8–$20/year using registrars like Namecheap or GoDaddy.
  3. Set Up DNS Records: Configure SPF, DKIM, and DMARC to authenticate your emails.
  4. Create Mailboxes: Use personalized names (e.g., john.doe@yourdomain.com) and avoid generic ones like info@.
  5. Warm Up Mailboxes: Gradually increase email volume over 8–12 weeks to build trust with email providers.
• Tools to Simplify the Process:
  • Mailforge: Automates DNS setup, mailbox creation, and domain management, saving time and reducing errors.
• Best Practices:
  • Keep email lists clean to avoid bounces.
  • Monitor deliverability metrics (open rates, spam complaints).
  • Follow compliance rules (accurate sender info, opt-outs, etc.).

Setting up custom domains takes effort, but it’s essential for successful cold email campaigns. Protect your brand, stay compliant, and improve email performance - all while keeping your main domain safe.

Selecting and Registering a Custom Domain

Why Use a Separate Domain?

Using your main business domain for cold email campaigns can put your digital reputation at risk. Each email you send impacts your domain's standing with email providers. If your domain gets blacklisted, recovering it is a tough uphill battle. Even if your emails comply with all the rules, recipients marking them as spam can still harm your domain's reputation.

George Wauchope, Founder of Emailchaser, emphasizes this point:

"You should NOT send cold emails from your primary domain."

In June 2025, Wauchope suggested using secondary domains, such as george@getemailchaser.com, instead of name@emailchaser.com. This approach helps shield your primary domain from potential blacklisting caused by cold email mistakes.

A separate domain acts as a protective layer for your main domain. It ensures that your critical communications - like transactional emails and customer interactions - remain unaffected, even as your cold outreach campaigns run independently. Plus, this separation makes it easier to track the performance of your campaigns without mixing data from other email activities.

To maintain brand recognition, you can set up redirects from your outreach domain to your main domain. This way, recipients can easily connect your outreach efforts to your brand, while your primary domain stays safe.

How to Choose a Domain Name

When picking a domain for cold emails, it's important to keep it aligned with your primary domain to maintain brand credibility and recognition. Recipients are more likely to engage with domains that feel familiar and trustworthy.

One way to achieve this is by keeping your brand name but changing the domain extension. For instance, if your main domain is yourcompany.com, you could use variations like yourcompany.io, yourcompany.net, or yourcompany.tech. This keeps your branding consistent while creating the needed separation.

Here’s a quick breakdown of how different domain extensions perform in cold email campaigns:

Extension	Performance	Cost	Best For
.com	Reliable but flagged more quickly	Standard	Requires careful warm-up
.net	Well-regarded by email providers	Standard	Bulk email campaigns
.io	High deliverability; spammers avoid it due to cost	Higher	Established businesses
.co	Poor deliverability	Standard	Avoid for cold email

The .io extension is particularly effective because its higher cost deters spammers, making it less likely to trigger spam filters. Meanwhile, .net domains strike a good balance between affordability and performance, as they're widely accepted by email providers.

Your domain choice should also align with your industry and audience expectations. Do some research to understand what resonates with your prospects. Avoid anything that could be seen as offensive or unprofessional, as it directly impacts how your brand is perceived.

If possible, consider buying a second-hand domain that's at least a year old. Older domains tend to appear more trustworthy to spam filters. However, always check the domain's reputation before purchasing. Tools like Talos and MX Toolbox can help you ensure the domain has a clean track record.

Registering a Domain

Domain registration is generally affordable, with prices ranging from $10 to $20 per year, depending on the registrar and domain extension. Here’s a look at current pricing from leading US-based registrars:

• GoDaddy: .com domains starting at $11.99/year.
• Namecheap: .com domains from $8.88/year.
• Domain.com: Starting at $9.99/year.
• Bluehost: Charges $12.99/year.

For a budget-friendly option, Cloudflare offers domain registration at near-wholesale prices if you don’t need additional services.

The registration process is pretty straightforward. Search for your desired domain name, add it to your cart, and complete the purchase by entering your contact details. Many registrars also offer domain privacy protection for an extra fee, which keeps your personal information hidden in WHOIS databases.

Once you’ve purchased your domain, you’ll need to point it to your email hosting server by updating the DNS records. After that, configure the necessary DNS settings to authenticate your emails and ensure smooth delivery.

Configuring DNS Records for Email Authentication

Once you’ve registered your domain, the next crucial step is setting up DNS records to authenticate your emails. Without proper authentication, your cold emails could easily end up flagged as spam.

Key DNS Records: SPF, DKIM, and DMARC

To ensure your emails are trustworthy and secure, you’ll need to configure three essential DNS records: SPF, DKIM, and DMARC. Here’s how each works:

• SPF (Sender Policy Framework): Think of SPF as your domain’s “approved sender” list. It tells receiving servers which IP addresses or mail servers are allowed to send emails on behalf of your domain. When an email reaches the recipient server, the server checks your SPF record to verify if the sender is authorized.
• DKIM (DomainKeys Identified Mail): DKIM adds a digital signature to your emails. This signature is generated using a private key, while the corresponding public key is stored in your DNS records. If the email is altered during transit, the signature becomes invalid, signaling potential tampering.
• DMARC (Domain-based Message Authentication, Reporting & Conformance): DMARC builds on SPF and DKIM by defining how receiving servers should handle emails that fail authentication. It lets you specify actions like delivering, quarantining, or rejecting unauthenticated messages.

Here’s a quick breakdown of these protocols:

Protocol	Purpose	How It Works	Security Benefit
SPF	Verifies authorized senders	Lists approved IPs in DNS	Helps prevent spoofing
DKIM	Confirms sender identity	Adds a digital signature to emails	Protects against tampering
DMARC	Manages failed checks	Sets rules for handling SPF/DKIM failures	Safeguards email integrity

Phishing attacks are a serious concern - 85% of cyberattacks in 2022 involved phishing, and 60% of emails employees received were designed to steal credentials. By implementing SPF, DKIM, and DMARC, you create a layered defense system that not only protects your domain but also improves your email deliverability.

To configure these records, log in to your domain’s DNS management panel:

• SPF: Add a TXT record listing all mail servers authorized to send emails on your behalf.
• DKIM: Generate a key pair through your email service provider and publish the public key as a TXT record.
• DMARC: Create a TXT record with your DMARC policy. Start with a "none" policy to monitor email traffic before enforcing stricter rules.

Marcel Becker, Senior Director of Product Management at Yahoo, highlights the importance of DMARC:

"The end goal is ideally a policy of p=reject. That's what DMARC is for. Ensuring that your domain cannot be spoofed and protecting our mutual customers from abuse."

Once these records are in place, you can move on to setting up tracking with CNAME records.

Setting Up Tracking with CNAME Records

CNAME records play a key role in email tracking and maintaining your brand’s identity. These records create aliases for your domain that redirect to your email provider’s tracking servers. For instance, you might set up an alias like "track.yourdomain.com" to monitor email opens, clicks, and unsubscribes.

Your email service provider will supply the necessary CNAME records for tracking. Be sure to verify your DNS entries after setting them up. Keep in mind that DNS changes can take up to 48 hours to propagate, even if everything is configured correctly.

Automating DNS Setup with Mailforge

Managing DNS records manually can be daunting, especially as your business grows. That’s where Mailforge comes in. This tool automates DNS configuration, handling all the necessary authentication records - SPF, DKIM, and DMARC - on your behalf. By automating these processes, Mailforge reduces the risk of errors and simplifies setup, making it especially useful for agencies or enterprises managing multiple domains.

Mailforge also offers a bulk DNS update feature, allowing you to apply changes across multiple domains at once. For example, if you need to update your SPF record to include a new mail server, you can roll out the change across all your domains with a single action.

For businesses requiring more tailored solutions, Infraforge provides private email infrastructure with advanced DNS customization. By automating DNS settings with Mailforge, you can maintain your domain's reputation while scaling your cold email campaigns efficiently.

Creating and Configuring Mailboxes

Once your DNS records are set up, it’s time to create mailboxes for your cold outreach campaigns. This step is crucial - it impacts how recipients perceive your emails and plays a big role in deliverability.

Mailbox Setup and Naming Conventions

Your mailbox name is more than just an address; it’s the first impression recipients get of your email. A professional, personal name can make all the difference.

Choosing the Right Names

Avoid generic addresses like "info@yourdomain.com" or "sales@yourdomain.com." Instead, opt for personalized names like "clark.kent@thedailyplanet.com." Personalized addresses feel more trustworthy and are more likely to get a positive response.

If you plan to scale your campaigns with multiple mailboxes, keep your naming consistent. For instance, if you use first and last names, stick to that pattern across all mailboxes. This consistency reinforces your brand identity and helps spam filters recognize your email infrastructure as legitimate.

Using Alternate Domains

If your main domain is "colliber.com", consider using variations like "colliber.co" or "colliber.io" for your cold email campaigns. These alternate domains protect your primary domain's reputation while maintaining recognition.

Scaling Your Email Setup

When scaling, diversify everything - domains, mailboxes, and providers. Don’t rely on a single provider or create all mailboxes under one Google Workspace admin. Spread your infrastructure across multiple providers to safeguard your operation if one account gets flagged or experiences issues.

Technical Setup Steps

Once you’ve chosen your domain and naming strategy, point your domain to your email host by updating the nameservers in your domain provider’s DNS settings. Popular hosts for cold outreach include Google Workspace, Microsoft Outlook, and specialized platforms like Mailforge and Infraforge.

Platforms like Mailforge can simplify scaling by automating bulk mailbox creation, allowing you to set up hundreds of mailboxes in minutes. After this, the next critical step is warming up your mailboxes to build sender reputation.

Mailbox Warm-Up

Setting up mailboxes is just the beginning. To ensure your emails land in inboxes (not spam folders), you’ll need to warm them up. This process gradually builds trust with email providers.

How Warm-Up Works

Warming up involves slowly increasing the number of emails you send while creating positive engagement patterns. This process typically takes 8 to 12 weeks and proves to providers like Gmail and Outlook that your emails are legitimate.

The warm-up process focuses on four activities: sending emails, receiving replies, getting emails from others, and replying to those emails. These activities mimic natural email behavior, making your mailboxes appear authentic to spam filters.

Step-by-Step Warm-Up Strategy

Start small - send 2-3 emails daily to people you know and trust. Ask them to reply, as early engagement is key to building a strong sender reputation. When they respond, reply back to keep the conversation going.

Gradually increase your sending volume by 1-2 emails every few days. Over 2-3 weeks, you’ll build up your sending capacity without triggering spam filters. Consistency is key - sending a stable number of emails daily helps providers recognize your patterns.

Once the initial warm-up period is over, keep the momentum going. Even when sending 30 cold emails daily, reserve some volume - like 20 emails - for warm-up activity. This ongoing process is especially important when launching new campaigns or switching domains.

Why Warm-Up Matters

Investing time in warming up your mailboxes pays off. A properly warmed-up domain can boost deliverability rates by up to 10%, open rates by 20%, and reply rates by as much as 15%. These improvements lead to more conversations and better results for your campaigns.

Tips for Effective Warm-Up

• Keep your warm-up emails short, personal, and natural. Avoid spammy words like "guaranteed" or "cheap".
• Use your business domain, not personal email services like Gmail or Yahoo.
• Ensure your DNS records (SPF, DKIM, and DMARC) are correctly configured before starting.

Track key metrics like inbox placement rates, open rates, bounce rates, and spam flags during the warm-up phase. Monitoring these helps you spot issues early and adjust your strategy.

For businesses managing multiple mailboxes, tools like Warmforge automate the warm-up process across domains. This ensures consistent sender reputation building without requiring manual effort.

Common Mistakes to Avoid

• Sending too many emails too quickly
• Skipping email authentication
• Using your main website domain for cold outreach
• Inconsistent warm-up activity

Avoiding these errors helps strengthen your sender reputation and sets the stage for successful email campaigns.

Scaling and Managing Multiple Domains and Mailboxes

Managing domains and mailboxes efficiently is crucial for maintaining cold email deliverability and safeguarding your brand’s reputation. As your campaigns expand, handling multiple domains and mailboxes becomes increasingly complex. A key strategy is to diversify your email providers and avoid relying on a single administrator. This approach not only reduces risks but also sets the foundation for cost-effective scaling.

When scaling, the math is straightforward: as the number of emails you send increases, so do the costs, since additional domains and mailboxes are required. Some experts suggest limiting each domain to 2–3 mailboxes, with each sending around 30 emails daily, while others recommend 5–6 mailboxes per domain, sending 50–70 emails per day, to optimize deliverability.

Bulk Management and Scaling with Mailforge

Setting up domains and mailboxes manually can be time-consuming, especially when configuring DNS records and authentication protocols like SPF, DKIM, and DMARC. Mailforge simplifies this process by automating these technical setups, making it up to 100 times faster than traditional methods. With Mailforge, you can manage hundreds of domains and mailboxes from a single dashboard.

"Procedures that usually took hours (setting DKIM, SPF, etc. records) for multiple domains, now take a few minutes. Mailforge is also cost-efficient since you spend per mailbox ~3 times less than with Gmail."

Mailforge also offers multiple workspaces, enabling you to organize projects and move domains or mailboxes between them with ease. Pricing starts at just $3 per mailbox per month, with bulk rates as low as $1.67 per mailbox. The platform even includes a planning tool to help you calculate exactly how many domains and mailboxes you’ll need based on your email volume. With a 4.8 out of 5 rating on G2 and over 10,000 businesses using its services, Mailforge is praised for its automation and simplicity.

"The simplicity and the automation in the buying process of domains, DNS setting, inbox creation, forwarding, etc. Everything in one place."

Next, let’s dive into the key metrics you should monitor as you scale your email campaigns across multiple domains.

Monitoring Deliverability Across Domains

Keeping an eye on email deliverability is essential to avoid problems. On average, email deliverability hovers around 81%, meaning nearly 1 in 5 emails could land in spam folders. To maintain healthy campaigns, it’s critical to track metrics like delivery rate, bounce rate, spam complaint rate, open rate, click-through rate, unsubscribe rate, inbox placement rate, and sender reputation.

"Everyone's goal is obviously 100%. What we focus on is our inbox placement. We want 100% of our emails getting to the inbox, and if it drops below 90%, we're going to immediately investigate what's going on."

Use free tools like Google Postmaster Tools, Microsoft SNDS, and Mail.ru Postmaster to monitor the health of your domains. Seed testing - sending test emails to providers like Gmail, Outlook, and Yahoo - can help confirm inbox placement. Regularly clean your email lists by removing inactive or invalid addresses; even one poor-quality list can negatively affect multiple domains.

It’s also important to monitor performance across all domains. If you notice issues, such as inbox placement dropping below 90%, act quickly to replace underperforming domains and adjust your sending practices using ISP feedback loops. Automation tools that track these metrics across your setup can save time and help ensure consistent campaign results.

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Compliance and Deliverability Best Practices

Staying legally compliant is a cornerstone of successful cold email campaigns. Ignoring regulations can tarnish your sender reputation, while following the rules can improve your chances of landing in your recipient's inbox. Below, we’ll break down key compliance guidelines and technical strategies to help you maintain both legality and deliverability.

Following the CAN-SPAM Act

The CAN-SPAM Act regulates all commercial emails in the U.S., including business-to-business messages. Whether you’re reaching out to consumers or other businesses, every cold email you send must meet these requirements:

• Accurate header information: Ensure your "From", "To", "Reply-To", and routing details - including your custom domain and email address - clearly identify you as the sender.
• Honest subject lines: Avoid clickbait or misleading promises. Your subject line should accurately represent the content of your email.
• Advertising disclosure: Clearly indicate that your email is an advertisement, but do so in a way that feels natural within the email copy.
• Physical address inclusion: Include your valid physical postal address in every email to establish trust with recipients.
• Opt-out mechanism: Provide an easy way for recipients to unsubscribe from future emails. Opt-out requests should remain valid for at least 30 days after the email is sent, and you must honor these requests within 10 business days.

Here’s a quick comparison of major regulations across different regions:

Regulation	Region	Primary Requirements	Penalties for Violation
CAN-SPAM	United States	Truthful sender info, accurate subject lines, physical address, opt-out	Up to $53,088 per violation
GDPR	European Union	Legitimate interest, transparency, opt-out, secure data storage	Up to €20 million or 4% of annual global turnover
CASL	Canada	Obtain consent, clear sender ID, opt-out, secure data storage	Up to $1 million (individuals) / $10 million (companies) per violation
CCPA	California, USA	Right to correct/delete data, opt-out of collection, "Do Not Sell" page	Up to $2,500 (unintentional) / $7,500 (intentional) per email

Note: These regulations are especially important for businesses operating globally.

Deliverability Optimization Tips

Following regulations is only part of the equation - getting your emails into inboxes is just as critical. Here are some proven strategies to enhance deliverability:

• Aim for high deliverability rates: Cold emails should hit inboxes at a rate of 95%–98%, exceeding the 85%–95% average for general marketing emails.
• Warm up your domain: Gradually increase your email volume over 8–12 weeks to build trust with email providers.
• Authenticate your emails: Regularly check your email authentication records (e.g., SPF, DKIM, DMARC) to ensure proper setup.
• Personalize your content: Emails with personalized subject lines can see a 47% boost in open rates, and adding details like the recipient’s name or company can increase engagement by 22%.
• Maintain clean email lists: Email lists can degrade by 22.5% annually. Remove bounced, unsubscribed, or inactive contacts to keep your list healthy and maintain open rates above 35%.
• Limit follow-ups: Sending more than one follow-up per week - or more than four total - can increase spam complaints by 38%.
• Provide a real reply address: Use a valid email address tied to your custom domain to encourage responses and improve credibility.
• Protect your domain reputation: Your domain’s reputation affects how email providers view your brand across platforms. Regularly monitor and maintain it for long-term success.

Conclusion

Setting up a custom domain for cold email campaigns is all about ensuring security and high deliverability. While the process can be intricate, it plays a critical role in protecting your brand and increasing the chances of your emails landing in inboxes - not spam folders. This involves steps like registering separate domains, configuring DNS records (SPF, DKIM, and DMARC), creating appropriately named mailboxes, and adhering to compliance standards.

As Reio Suun highlights, achieving optimal domain authentication requires careful adjustments and fine-tuning. This challenge becomes even greater when you're tasked with managing dozens - or even hundreds - of domains manually.

Thankfully, tools like Mailforge are designed to streamline this process. These automation solutions can handle DNS configuration and set up your email infrastructure in just minutes. Plus, they can cut mailbox costs by nearly three times compared to traditional providers.

To ensure success, stick to the basics, whether you're managing a single domain or hundreds. Start by warming up your domains for 2–3 weeks before launching campaigns. Make sure your email authentication is solid, segment your leads thoughtfully, and test your deliverability before going live. As discussed earlier, maintaining a strong domain reputation is a proactive effort - once it's damaged, recovery is tough.

Compliance is non-negotiable, especially with CAN-SPAM penalties reaching up to $43,792 per email. Gradual warm-up, strict adherence to regulations, and ongoing monitoring are essential for sustainable cold email practices.

The formula is straightforward: use separate domains, authenticate emails correctly, warm up gradually, and stay compliant. Scaling these practices efficiently is what sets successful campaigns apart.

FAQs

Why is it important to use a custom domain for cold email campaigns?

Using a custom domain for cold email campaigns is a smart move to protect your primary domain's reputation and improve email deliverability. When you send emails from your main domain, there's always a risk of being flagged as spam. If that happens, it can damage your brand's credibility and result in all emails from that domain landing in spam folders - a scenario no business wants.

A custom domain gives you more control over your email-sending practices, making it easier to manage your sender reputation. It also reduces the risk of legal or reputational problems that can occur if a generic domain gets linked to spam or other harmful activities. By opting for a custom domain, you not only protect your primary domain but also set the stage for more successful outreach campaigns.

What are SPF, DKIM, and DMARC, and how do they improve email deliverability?

SPF, DKIM, and DMARC: The Email Authentication Trio

SPF, DKIM, and DMARC are three key protocols designed to improve email deliverability while safeguarding against phishing and spoofing attacks. Here's how they work:

• SPF (Sender Policy Framework): This protocol allows domain owners to specify which mail servers are permitted to send emails on their behalf. By doing so, it helps reduce cases of unauthorized use of their domain.
• DKIM (DomainKeys Identified Mail): DKIM ensures that the content of an email remains intact during transit. It does this by attaching a digital signature to the email, which the recipient's mail server can verify for authenticity.
• DMARC (Domain-based Message Authentication, Reporting & Conformance): Building on SPF and DKIM, DMARC gives domain owners control over how emails failing authentication checks are handled. It can instruct mail servers to reject, quarantine, or accept such emails, adding an extra layer of protection.

When used together, these protocols not only help your emails land in the right inbox but also shield your domain from fraud and misuse, reinforcing trust in your communications.

Why is warming up your mailbox important for maintaining a strong sender reputation?

Warming up your mailbox is a crucial step in establishing a good sender reputation with email service providers (ESPs). By slowly ramping up your email activity over time, you demonstrate that your account is legitimate and reliable. This approach helps avoid the common pitfall of being flagged as spam, which often occurs when a new account sends out a large volume of emails too quickly.

Taking the time to warm up your mailbox also boosts email deliverability, increasing the chances that your messages will land in recipients' inboxes instead of their spam folders. ESPs assess sender reputation using factors like open rates, replies, and consistent sending patterns. A proper warm-up process lays the groundwork for successful cold email campaigns and higher engagement rates.

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• Common Cold Email Infrastructure Problems Solved
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