Should you use your primary domain or secondary domains for cold email outreach? Here's the answer: always use secondary domains. Sending cold emails from your primary domain risks blacklisting, which can disrupt critical business communications and damage your brand's reputation. Secondary domains, on the other hand, provide a safer, scalable way to manage outreach campaigns.
Key points to know:
Why Secondary Domains Work Better:
Costs: Secondary domains cost ~$12–32/year + ~$4–6/mailbox/month, while primary domains are ~$6–12/user/month.
Setup Tip: Warm up new domains for 15 days before scaling. Use tools like Mailforge to automate DNS setup and manage multiple domains efficiently.
Quick Comparison:
| Factor | Primary Domain | Secondary Domain |
|---|---|---|
| Deliverability Risk | High | Low |
| Scalability | Limited (40–50/day) | High (40–50/day/domain) |
| Setup Time | Immediate | ~15 days (warming up) |
| Cost | $6–12/user/month | $12–32/year + $4–6/mailbox |
Using secondary domains is the smarter, safer approach for scaling cold email campaigns.
A primary domain is the digital backbone of your business. It’s what identifies your website and official email addresses. For example, if your business is called TechSolutions, your primary domain might be techsolutions.com, and your team’s emails would look like john@techsolutions.com or support@techsolutions.com.
This domain isn’t just a web address - it’s a cornerstone of your brand’s reputation. Customers, partners, and prospects immediately associate emails from your primary domain with your business, giving them a sense of reliability and trust.
"Your primary domain is your brand's core digital identity. It deserves protection."
Primary domains play a key role in building your brand’s identity. Emails sent from your domain create a sense of trust and professionalism, as recipients can instantly recognize them as coming from a legitimate business.
Using your primary domain for email communications also gives your company a polished, professional image - something that’s crucial when working with enterprise clients or handling sensitive matters. It shows attention to detail and reinforces your credibility.
Another advantage is the simplicity it brings to email management. With all communications centralized under one domain, it’s easier for recipients to recognize and whitelist your emails, ensuring they land in the inbox rather than the spam folder. However, while this setup is ideal for regular business interactions, using your primary domain for cold outreach can backfire.
When it comes to cold email campaigns, primary domains can quickly become a liability. The biggest risk? Domain blacklisting. If email providers flag your domain as spam, all future emails - whether they’re sales pitches or customer support messages - may end up in spam folders.
"You should NOT send cold emails from your primary domain." - George Wauchope, Founder of Emailchaser
Here’s why this happens: cold emails often go to recipients unfamiliar with your brand. If they mark your messages as spam, email providers start associating your domain with unwanted mail. Once blacklisted, every email tied to your primary domain - whether it’s from sales, support, or billing - gets affected. This can seriously undermine your business communications.
The fallout doesn’t stop there. A blacklisted domain can also hurt your website’s SEO, dragging down your search rankings. Cold email campaigns tend to have higher bounce rates and complaint ratios, which makes your primary domain especially vulnerable to reputation damage.
Recovering from a blacklisted domain is no small feat. It’s a lengthy, challenging process that involves rebuilding your sender reputation from scratch. Meanwhile, your business suffers as vital communications are disrupted. To avoid this headache, it’s crucial to use a secondary domain for cold email campaigns.
"Cold emailing without a dedicated domain is a rookie mistake. In 2025, using a separate cold email domain is essential to avoid spam issues." - Mailreach.co
Secondary domains are additional domain names businesses use exclusively for cold email outreach, keeping them separate from the primary domain. Think of them as protective layers that shield your main domain from potential risks.
"The domains that you use to send cold emails (other than your primary domain) are called secondary domains." - Dhruv Patel
The idea is simple: these domains handle all cold email campaigns, leaving your main domain untouched by any reputation issues. Unlike subdomains or email aliases, which are tied to your primary domain, secondary domains operate independently with their own mail servers and sender reputations. This separation ensures that if a campaign encounters problems, like being flagged as spam, your primary domain remains secure.
Secondary domains also make it easier to scale your outreach. By using multiple secondary domains, you can spread your campaigns across them, reducing the risk of any single domain being flagged. This setup allows businesses to contact thousands of prospects each day without compromising the integrity of their primary domain.
Secondary domains offer several advantages when it comes to cold email outreach:
"Distributing your cold email campaigns over several domains can dramatically up your deliverability, and subsequently, those all-important reply rates. And that means? Yep, more revenue!" - Mails.ai
While secondary domains offer many benefits, setting them up and managing them requires careful planning:
For businesses planning to scale, tools like Mailforge can simplify the management of secondary domains. Features like automated DNS setup, domain warming, and bulk management make it easier to handle hundreds or even thousands of domains. These tools reduce the technical burden while optimizing your campaign performance, creating a solid foundation for scaling - details of which are covered in the next section.
When choosing between primary and secondary domains for cold email campaigns, it’s important to weigh the differences. Here’s a side-by-side comparison:
| Factor | Primary Domain | Secondary Domain |
|---|---|---|
| Cost | ~$6–12 per user/month (Google Workspace/Microsoft 365) | ~$12–32 per domain/year + ~$4–6 per mailbox/month |
| Deliverability Risk | High – affects all business communications | Lower – risk is isolated from core business emails |
| Management Complexity | Simple – single domain setup | Moderate – requires setup and ongoing monitoring |
| Scalability | Limited by reputation constraints | High – each domain adds 40–50 emails/day |
| Setup Time | Immediate – already configured | ~15 days – gradual warming up needed |
| Reputation Impact | Critical – directly tied to brand credibility | Contained – protects the primary domain's reputation |
| Email Volume Capacity | 40–50 emails/day safely | 40–50 emails/day per domain (scales with more domains) |
Let’s explore these factors in more detail.
Cost: Primary domains typically cost $6–12 per user/month through services like Google Workspace or Microsoft 365. Secondary domains, on the other hand, involve an annual registration fee of $12–32 per domain, plus mailbox costs of $4–6 per month. While secondary domains may seem like an added expense, they provide a safeguard against the potential risks of blacklisting your main domain.
Deliverability Risk: Using your primary domain for cold outreach carries substantial risk. Any spam complaints or negative feedback could harm all your business communications . Secondary domains are designed to mitigate this risk, offering an isolated environment for outreach. In fact, 61% of marketers rely on secondary domains to protect their primary domain during email campaigns.
Management Complexity: Primary domains require minimal effort to manage since they’re already configured for regular communication. Secondary domains, however, demand more attention. Each domain must be properly configured with SPF, DKIM, and DMARC records and gradually warmed up over 15 days to build credibility. Tools like Mailforge simplify these tasks by automating DNS setup and managing multiple domains, making large-scale campaigns easier to manage.
Scalability: Primary domains are limited to sending 40–50 emails daily to maintain a good reputation. Secondary domains eliminate this bottleneck - each domain adds another 40–50 emails per day, allowing you to scale your outreach significantly while keeping sending patterns natural.
Setup Time: Primary domains are ready to use immediately, as they’re pre-configured for business needs. Secondary domains, however, require a warming period of about 15 days to establish trust with email providers. While this takes extra time, it lays a solid foundation for large-scale campaigns.
Reputation Impact: Your primary domain directly reflects your brand. Any issues with deliverability or spam complaints can damage your credibility. Secondary domains act as a buffer, ensuring that your main domain remains unaffected by aggressive outreach efforts.
Email Volume Capacity: Primary domains cap safe email sending at 40–50 emails per day. Secondary domains allow you to scale, as each additional domain provides the same daily capacity. This makes secondary domains a practical choice for businesses aiming to expand their outreach.
When setting up secondary domains, it's important to take steps that protect your primary domain while ensuring your outreach efforts are effective. Start by selecting domain names that are simple, memorable, and align with your brand. Stick to trusted extensions like .com, .net, or country-specific ones such as .co.uk if you're targeting specific regions. For a modern twist, consider brand-related extensions like yourcompany.io, or use prefixes and suffixes, such as getyourcompany.com, which work well for larger email campaigns.
Once your domain is registered, take care of authentication. Set up SPF, DKIM, and DMARC to establish credibility and protect your emails. As Dhruv Patel from Saleshandy puts it:
"For authentication, you have to set up SPF, DKIM, and DMARC, which will help you protect the emails and give the right signals to the ESPs about your authenticity."
Use personal-sounding email aliases, like jane@yournewdomain.com, instead of generic ones, to create a more approachable tone. To maintain optimal sending practices, limit each domain to a maximum of five email accounts. This helps avoid overloading the domain and keeps sending patterns natural.
Building a solid sender reputation takes time and a well-planned warm-up process. Begin by sending 10–20 emails per day, gradually increasing the volume over three weeks. Monitor bounce rates and complaints closely during this period. Start with your most engaged contacts, using personalized messages to encourage actions like opens, clicks, and replies.
Stay active in conversations by responding to replies, and regularly check your domain's reputation using tools like Google Postmaster Tools and Microsoft SNDS. Keep your email lists clean by removing invalid or unengaged addresses. If you encounter deliverability issues with any account, pause its activity and allow for further warm-up.
Once your domains are warmed up and performing consistently, managing them efficiently becomes crucial. This is where automation comes into play.
Handling multiple secondary domains manually can be time-consuming and complex. Automation tools simplify the process, especially when it comes to setting up and managing authentication records like SPF, DKIM, and DMARC.
Platforms like Mailforge automate DNS configuration, enabling you to create and manage hundreds - or even thousands - of domains in just minutes. These tools take care of authentication setup, eliminating the technical guesswork.
Automation goes beyond setup. It optimizes email scheduling, ensuring messages are sent when recipients are most likely to engage. It also helps rotate out problematic domains without disrupting your campaigns. Automated warm-up sequences gradually increase email volume, building a strong sender reputation without the need for constant manual adjustments.
Additionally, automation tools provide detailed analytics on campaign performance, including open rates, click-through rates, and replies. This data allows you to refine your outreach strategy. Automated email sequences ensure consistent follow-ups, saving time while keeping prospects engaged.
For businesses of all sizes - whether agencies managing multiple client campaigns or enterprises scaling across different markets - platforms like Mailforge offer advanced features like SSL, domain masking, bulk DNS updates, and compatibility with various sending software. These tools streamline operations and enhance deliverability.
Scaling cold email campaigns isn’t just about sending more emails - it’s about protecting your brand while doing so. Using your primary domain for cold outreach might seem convenient, but it puts your entire business communication system at risk. If your primary domain gets blacklisted, it can disrupt everything from customer support emails to internal communications. That’s a risk no business can afford.
As George Wauchope, Founder of Emailchaser, highlights, primary domains should never be used for cold outreach. If flagged, your sender reputation takes a hit, and major email providers like Gmail and Outlook may mark all emails from your primary domain as spam. Once that happens, recovering your reputation is nearly impossible.
This is where secondary domains come in. They act as a safety net, shielding your primary domain from potential blacklisting. If a secondary domain gets flagged, it’s easy to replace without affecting your core business operations. For instance, sending 1,000 cold emails a day might require 7–10 secondary domains and 20–30 dedicated email addresses. This approach spreads the risk and ensures that your primary domain remains untouched.
Secondary domains also make scaling more affordable and efficient. Managing multiple domains manually can be a headache, requiring technical expertise and constant monitoring. Tools like Mailforge simplify this process. Starting at just $13 per month for mailbox slots, Mailforge automates domain management tasks like DNS setup, SPF, DKIM, and DMARC configuration, and even handles domain warm-ups. It allows businesses to manage hundreds or even thousands of domains in minutes, providing enhanced security and domain masking.
Another advantage of secondary domains is the ability to segment campaigns effectively. You can organize your outreach by team, campaign type, or audience, tailoring messages and tracking performance with precision. Even small teams can operate like large enterprises thanks to automation tools that remove the technical barriers.
For companies aiming to grow, secondary domains are not optional - they’re essential. They provide the safety, scalability, and cost-efficiency needed for sustainable cold email outreach. Simply put, secondary domains are the backbone of any successful cold email strategy.
Managing multiple secondary domains can be a smooth process if approached thoughtfully. Start by capping the daily email volume for each domain and spreading out your sends evenly. This helps maintain balance and prevents overloading any single domain. Take the time to gradually warm up each domain - this step is crucial for building a solid sending reputation and ensuring reliable email deliverability.
Automating repetitive tasks like setting up DNS records and monitoring the health of your domains can save you a lot of time and help avoid potential mistakes. Make it a habit to routinely check for any issues, such as blacklisting or sudden drops in deliverability. And remember, relying too heavily on one domain can harm its reputation, so distribute usage wisely to reduce risks.
To get a new secondary domain ready for email campaigns, start small. Send about 5–10 emails per day and gradually increase the number by 10–15% each day. The key here is engagement - craft emails with personalized and varied content to encourage responses and interactions. Avoid any sudden jumps in volume, as this could negatively impact your domain's reputation.
Initially, focus on sending emails manually. This helps build trust and establishes a positive reputation for your domain. Once your domain gains credibility, you can shift to automated sending. This warm-up process usually takes anywhere from a few weeks to a month to achieve the best results.
Using secondary domains for cold email outreach is a smart way to protect the reputation of your primary domain. By keeping outreach activities separate, you minimize the chances of spam complaints or delivery problems spilling over and affecting your main domain. This keeps your primary domain reliable and trusted for important communications.
Secondary domains also offer more flexibility when scaling your outreach campaigns. They let you send emails from multiple addresses without overwhelming a single domain, which helps improve email deliverability and overall campaign results. This approach is especially helpful for businesses aiming to grow their cold email efforts while preserving a professional and trustworthy sender reputation.