Scaling Domains and Mailboxes: Best Practices

Scaling email campaigns without harming your domain's reputation requires spreading the workload across multiple domains and mailboxes. Here's the key takeaway: limit each mailbox to 30–50 emails daily and use tools to automate setup and monitoring. This approach ensures better deliverability, protects your primary domain, and keeps your campaigns running smoothly.

Quick Tips:

• Use multiple domains: For 10,000 emails/month, split across 5–10 domains and 20–30 mailboxes.
• Warm up mailboxes: Gradually increase sending volume over 4–8 weeks.
• Automate DNS setup: Tools like Mailforge handle SPF, DKIM, and DMARC records in minutes.
• Monitor metrics: Keep bounce rates under 2% and spam complaints below 0.3%.
• Rotate domains regularly: Domains typically last 4–6 months before performance drops.

Scaling email infrastructure effectively is about balancing volume, automation, and domain health. Follow these steps to maintain high inbox placement rates and protect your outreach efforts.

Domain and Mailbox Scaling Basics

What Is Domain and Mailbox Scaling?

Domain and mailbox scaling is a method used to manage high-volume cold email campaigns without triggering spam filters. Instead of relying on a single domain to send thousands of emails - which could harm your domain's reputation - this approach spreads the workload across multiple custom domains. Each domain typically has 2–4 dedicated mailboxes.

Here’s how it works: Each mailbox sends about 30–40 emails daily after a short warm-up period to mimic organic email activity. For example, using 10 domains with 3 mailboxes each, sending 30 emails per day, results in approximately 900 emails daily. This setup not only protects your primary domain but also allows for the scale needed in B2B lead generation.

To further enhance deliverability, use personalized email addresses like firstname.lastname@domain.com rather than generic ones like info@ or sales@. Additionally, consider purchasing domains similar to your main brand (e.g., getshrimp.com if your primary domain is shrimp.com) specifically for outbound campaigns. This strategy minimizes the risk of spam triggers while maintaining your main domain's integrity.

Benefits of Scaling Your Email Infrastructure

Scaling your email infrastructure offers multiple advantages, from increased sending capacity to better performance. A well-structured system allows you to send between 900 and 1,000+ emails daily while maintaining high inbox placement rates. This means more opportunities for conversations, meetings, and ultimately, a stronger return on investment from your outreach.

One major benefit is protecting your main domain's reputation. By keeping cold email campaigns separate from your primary domain, issues like deliverability problems on an outbound domain won’t interfere with important emails like customer support or transactional messages. Even if one mailbox gets flagged, the rest of your campaign can continue uninterrupted.

From a performance standpoint, a scaled setup improves engagement metrics. By limiting the number of emails per mailbox (generally under 1% of the domain's monthly capacity) and gradually warming up mailboxes over a 2–3 week period, you establish a positive sender reputation. This approach not only reduces bounce rates but also boosts reply rates. Once warmed up, mailboxes can handle 50–150 emails daily - and even up to 200+ with a solid sending history.

Scaling also streamlines operations. Tasks like configuring DKIM, SPF, and DMARC records for each domain, which used to take hours, can now be completed in just minutes using automation tools. Isabella L., Founder of Let's Fearlessly Grow, highlights this efficiency:

"Operating in a high-growth startup environment requires speed, scalability, and operational efficiency. We needed to build an outbound motion that didn't break as we scaled - and Mailforge gave us that foundation."

Cost savings are another key advantage. Purpose-built tools for cold outreach are far more affordable than traditional email providers. For instance, setting up 200 mailboxes with a specialized platform costs about $484 per month, compared to $1,680 per month with Google Workspace or $1,200 per month with Microsoft 365. That’s nearly three times more cost-effective per mailbox.

How to Scale Domains and Mailboxes

Automating DNS Setup for Multiple Domains

Setting up DNS records manually for multiple domains can be a massive time drain. Each domain requires SPF, DKIM, and DMARC records to ensure your emails are authenticated and don't get flagged as spam. Now imagine doing this for 5, 10, or even 50 domains - it’s not just tedious; it’s a bottleneck.

Automating this process can save you hours. Tools like Mailforge offer a "Free Automated Set Up" feature, which takes care of creating and configuring all the necessary DNS records - SPF, DKIM, DMARC, and even custom domain tracking. This automation ensures the setup aligns with best practices, so you don’t need to be a DNS expert to get it right.

For ongoing adjustments, bulk DNS update tools are a game-changer. They let you tweak records across multiple domains with just a few clicks, which is especially handy when you need to quickly update configurations or rotate infrastructure. A good tip: start your DMARC policy at "none" to monitor activity, then gradually move to "quarantine" or "reject" as your domains gain trust. Use tools like MXToolbox or Google Postmaster to double-check your records.

Once you've automated DNS setup, the next focus is optimizing your mailboxes to ensure your emails land in the inbox, not the spam folder.

Configuring Mailboxes for Better Deliverability

Proper mailbox configuration is critical for ensuring your emails actually reach their destination. Each mailbox must have SPF, DKIM, and DMARC records on its domain to prove the emails are legitimate.

Here’s a smart approach: set up 2–3 mailboxes per domain using dedicated and verified email accounts. It’s also wise to use separate sending domains that aren’t tied to your primary brand. Stick with reliable domain extensions like .com, .io, or country-specific TLDs. Avoid extensions like .biz or .online, and steer clear of domains with hyphens or numbers - they tend to perform poorly in cold email campaigns.

Start small: send just 1–2 emails per day from each mailbox. Gradually increase this volume by 20–50% daily over 4–8 weeks until you’re sending 50–100 emails per day per mailbox. Platforms like Google Workspace often cap cold email sending at 30–100 emails per day per mailbox, so keep your total volume - including warm-up emails - within this range. Watch your bounce rates closely; anything over 2% could signal issues with your email list that need immediate attention.

Here’s how you might scale up your email sending:

For example, if you need to send 10,000 emails per month (around 333 per day), you could use 5–10 domains with 20–50 mailboxes in total. A balanced setup might involve 5 domains with 4 mailboxes each, sending 40–50 emails per day per mailbox. This distribution helps prevent any single domain from being overwhelmed.

Once your mailboxes are set up and running smoothly, the next step is to protect your primary domain with domain masking.

Using Domain Masking to Protect Sender Identity

After automating DNS and fine-tuning your mailboxes, the final step to scaling your email infrastructure is safeguarding your sender identity with domain masking. This technique allows you to display branded websites while keeping your primary domain hidden, adding an extra layer of protection.

Why is this important? When sending large volumes of cold emails, separating your main domain from your sending domains ensures that if one domain gets flagged, your core brand remains untouched.

Here’s how it works: create lookalike domains that resemble your brand but aren’t identical. For example, if your main domain is shrimp.com, you could use getshrimp.com or tryShrimpApp.com for your campaigns. These alternatives maintain brand recognition while shielding your primary domain. Stick with trusted extensions like .com or .net, avoiding less familiar ones like .co, which can confuse recipients.

For added security, pair domain masking with SSL certificates. This ensures your domains are secure and private, even as you scale up your efforts. New domains should be aged for at least 30 days - ideally 3 months - before heavy use, giving them time to build a solid reputation. Keep a reserve of warmed-up domains ready for rotation, as active sending domains can burn out after 4–6 months.

Managing Scaled Email Infrastructure

Building a scaled email setup is just the beginning. The real challenge lies in maintaining its health over time. Managing dozens - or even hundreds - of domains and mailboxes demands constant attention to warming up accounts, monitoring reputation, and rotating resources. Skipping these steps can lead to a rapid drop in deliverability. Here's how to effectively warm up, monitor, and rotate mailboxes to keep your email campaigns running smoothly.

Warming Up Multiple Mailboxes

When you set up a new mailbox, it needs a warmup period of 4–8 weeks. Start small: send just 1–2 emails per day and gradually increase to a target of 30–50 daily emails. A typical warmup schedule might look like this:

• Week 1: 1–3 emails daily
• Week 2: 5–10 emails daily
• Week 3: 15–20 emails daily
• Weeks 4–6: 25–40 emails daily

If you’re warming up several inboxes - say, 10 to 50 at once - stagger their start dates to create a more natural traffic pattern. Remember, warmup emails count toward your provider's daily limits. For example, Gmail includes both warmup and cold emails in their daily cap of 50 emails per account.

For large-scale operations, automation is your best friend. Tools like Warmforge can simulate realistic email activity - sending, receiving, and even generating replies - to help build reputation faster while saving you hours of manual effort. Once your mailboxes are warmed up, the next step is keeping a close eye on their performance.

Monitoring Domain Reputation and Preventing Burnout

Domains usually maintain a strong reputation for about 4–6 months, but pushing them too hard can lead to faster deterioration. To protect your email reputation, focus on key metrics like:

• Spam complaint rates: Keep these under 0.1–0.3%.
• Bounce rates: Anything above 5–7% is a red flag.
• Open and reply rates: Sudden drops here can signal a problem.

You’ll also want to check if your emails are landing in spam folders. Automated tools can simplify this process. Platforms like Google Postmaster Tools help track Gmail reputation, while MXToolbox can handle blacklist checks and DNS diagnostics.

If you notice high bounce rates, a spike in complaints, or a sudden drop in open rates, act fast. Pause sending from the affected mailbox, review your email lists for quality issues, and adjust your content strategy. Shift your email volume to healthier, pre-warmed domains or inboxes to avoid further damage. Ignoring these warning signs could lead to blacklisting, which is much harder to recover from.

Rotating Domains and Mailboxes

To keep your email system running smoothly, regular rotation of domains and mailboxes is essential. Stick to a limit of 30–50 cold emails per inbox daily, and assign one domain for every 2–3 inboxes. For example, instead of sending 200 emails from a single inbox, distribute them across five inboxes, sending about 40 emails per inbox.

A good rotation strategy ensures that each prospect is assigned to an inbox using methods like round-robin distribution or assigning specific pools to individual reps. Automation tools can skip inboxes that hit their daily limits or show signs of trouble, automatically switching to pre-warmed backups. This approach allows you to scale without interruptions.

It’s also smart to regularly purchase new domains and configure their DNS records properly from the start. Begin warming these domains at low volumes well in advance - ideally 4–8 weeks - so they’re ready when needed. Label domains in your inventory system as "warming", "ready", "active", or "retiring" to keep things organized. That way, if one domain starts to falter, you’ll have fresh capacity ready to take over without missing a beat.

Scaling with Mailforge

Mailforge Features for Scaled Outreach

When it’s time to take your outreach efforts to the next level, Mailforge simplifies the process with tools designed to save time and reduce complexity. For example, DNS configuration for SPF, DKIM, DMARC, and tracking records - which can normally take hours - is automated, cutting setup time down to just minutes.

Managing DNS settings across multiple domains can become a headache once you scale past 10–20 domains. Mailforge makes bulk DNS updates easy. Whether you need to update a tracking CNAME or tweak a DMARC policy, you can apply changes across 200 domains with a single click - no need to log into each DNS provider individually.

To protect your primary brand while maintaining professionalism, Mailforge offers SSL and domain masking. This allows you to send emails from secondary domains (like outreach-brand.com instead of brand.com) while using secure, branded HTTPS tracking links. This strategy not only safeguards your core domain’s reputation but also ensures your emails look credible to recipients.

Mailforge also supports multiple workspaces, giving you the flexibility to organize domains and mailboxes by client, campaign, or team. You can easily reassign resources as your needs evolve. Plus, since Mailforge integrates seamlessly with any sending software, you can keep using your preferred outreach platform, CRM, or sales engagement tool. This means your existing software can focus on what it does best - handling sequences, personalization, and scheduling.

Mailforge Pricing and Cost Structure

Mailforge doesn’t just offer powerful features - it also provides transparent and cost-effective pricing. The platform uses a slot-based pricing model, starting at $30 per month for 10 mailbox slots (billed monthly) or $25 per month for 10 mailbox slots (billed annually). This breaks down to about $2–$3 per mailbox per month. For larger setups, such as 200 mailboxes, Mailforge costs approximately $484 per month - a fraction of the cost compared to $1,680 per month with Google Workspace or $1,200 per month with Microsoft 365.

Domain pricing depends on the top-level domain (TLD) you select. For instance, five .com domains cost $70 per year, charged as a one-time fee. Additional features like SSL and domain masking cost $2 per domain per month (billed monthly) or $6 per domain per year (billed annually).

To get a clear estimate of your costs, you can use Mailforge's pricing calculator at https://mailforge.ai/pricing. Simply input your expected monthly email volume - such as 10,000 cold emails - and factor in a safe limit of 30–50 emails per inbox per day. The calculator will then show you the number of mailbox slots and domains you'll need, along with the total monthly cost in USD.

Conclusion

Scaling domains and mailboxes is about creating a reliable system, not just stacking up infrastructure. The secret to campaigns that consistently generate leads, instead of fizzling out, lies in three key areas: technical setup, automation, and regular upkeep.

Focus on the basics first. As outlined in this guide, setting up SPF, DKIM, and DMARC properly can push your deliverability rates to 85–95%. Use multiple domains - typically 2 to 5 - and spread your email volume across them. A good rule of thumb is sending 30–50 emails per inbox daily. Since domains generally last 4–6 months, rotating them regularly is essential.

Automation saves time and effort. Automating tasks like setting up DNS records, warming up mailboxes, and handling bulk updates can eliminate hours of manual work. Danny Goff, Director of Sales at Propeller, highlighted this efficiency:

"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".

This kind of time-saving becomes crucial when managing dozens - or even hundreds - of mailboxes.

Ongoing maintenance keeps campaigns on track. Use tools like Google Postmaster to keep an eye on your domain's reputation. Warm up new mailboxes gradually over 4–8 weeks, and always aim to keep bounce rates under 2%. A consistent, well-rounded approach ensures your outreach efforts remain scalable and effective.

FAQs

What steps can I take to protect my domain's reputation during email campaigns?

To make sure your domain maintains a good reputation during email campaigns, stick to these best practices:

• Authenticate your emails with key DNS records like DMARC, SPF, and DKIM. Tools like Mailforge can make this process easier by automating DNS setup.
• Write clean, relevant content by avoiding spammy language and focusing on concise, personalized messages.
• Gradually warm up your email addresses to build trust with email providers. Platforms like Warmforge can assist with this process to improve deliverability.
• Keep an eye on deliverability metrics so you can catch and fix potential issues before they escalate.

By responsibly managing your email infrastructure and keeping DNS records up to date, you can maintain a strong reputation and run successful campaigns.

How do I properly warm up new mailboxes for cold email outreach?

Warming up new mailboxes the right way involves a steady and strategic approach. Start small by sending emails to a select group of highly engaged contacts. This helps build a solid sender reputation from the get-go. Make sure your emails are personalized, relevant, and steer clear of anything that might come across as spammy.

Consistency plays a huge role here. Stick to a regular sending schedule and keep a close eye on key metrics like open rates, bounce rates, and any spam complaints. These numbers will give you a clear picture of how well your emails are being received. For an even smoother process, consider using specialized email warm-up tools - they can help boost your chances of landing in the inbox instead of the spam folder.

Why is rotating domains essential for email campaigns?

Rotating domains plays a crucial role in maintaining the success of your email campaigns. It helps protect your sender reputation and improves email deliverability. By distributing your emails across multiple domains, you lessen the risk of triggering spam filters or overloading a single domain with too much email traffic.

Another benefit? It reduces the likelihood of blacklisting, ensuring your campaigns continue to perform consistently while reaching your audience. This approach is especially valuable when scaling cold email outreach, as it helps keep your infrastructure secure and effective.

Related Blog Posts

• How to Set Up Multiple Email Domains in 5 Minutes
• Scaling Mailboxes for High-Volume Outreach
• How Mailbox Rotation Boosts Scalability
• How Domain Reputation Impacts Cold Email Success