Cold Email Infrastructure: How to Set Up Domains, Mailboxes and Sending
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Why Infrastructure Matters
Sending cold emails from your primary business domain is risky. If recipients mark your messages as spam or your bounce rate spikes, the reputation damage affects all email from that domain, including transactional emails, customer support and internal communications.
Dedicated cold email infrastructure separates your outreach activity from your business communications. If something goes wrong with your cold campaigns, your primary domain stays protected.
Step 1: Register Secondary Domains
Buy separate domains for cold outreach. These should be similar to your primary domain but distinct enough to keep your main domain isolated.
Domain selection
If your company domain is example.com, consider variations:
- tryexample.com
- getexample.com
- example.io
- examplehq.com
- helloexample.com
Guidelines:
- Keep the domains recognisable. When a recipient checks who sent the email, the domain should clearly relate to your brand.
- Avoid domains that look like phishing attempts. Do not use misleading names.
- Register through a reputable registrar.
- Buy 2-5 domains to start. This lets you distribute your sending volume and protect against any single domain being flagged.
Domain age
New domains have no reputation, which is different from bad reputation but still causes deliverability challenges. ISPs are more cautious with new domains. Allow at least 2-4 weeks before sending any cold email from a new domain. During this time, set up authentication and begin warm-up (covered below).
Step 2: Set Up Email Hosting
Each secondary domain needs email hosting. You need actual mailboxes that can send and receive email.
Hosting options
Google Workspace: Professional email hosting with good deliverability infrastructure. Supports custom domains. Sending limits apply (see How Many Cold Emails Per Day).
Microsoft 365: Similar to Google Workspace in features and deliverability. Supports custom domains with Exchange Online mailboxes.
Dedicated SMTP providers: Services like Amazon SES, Mailgun or SendGrid provide sending infrastructure. Better for higher volumes but require more configuration.
Mailbox setup
Create 2-3 mailboxes per domain. Each mailbox should have a real name and professional signature.
Example:
Do not use generic addresses (info@, sales@, noreply@) for cold outreach. Recipients respond better to messages from a real person.
Set up each mailbox with a profile photo and complete signature. Some receiving servers check for these as legitimacy signals.
Step 3: Configure DNS Authentication
DNS authentication records prove to receiving mail servers that your emails are genuinely from your domain and have not been tampered with. Without these, your emails are far more likely to land in spam.
SPF (Sender Policy Framework)
SPF tells receiving servers which IP addresses are authorised to send email on behalf of your domain.
How to set it up:
- Go to your domain's DNS settings.
- Add a TXT record.
- The value depends on your email provider.
For Google Workspace:
v=spf1 include:_spf.google.com ~all
For Microsoft 365:
v=spf1 include:spf.protection.outlook.com ~all
Important: You can only have one SPF record per domain. If you use multiple sending services, combine them in a single record:
v=spf1 include:_spf.google.com include:spf.protection.outlook.com ~all
DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to your outgoing emails. Receiving servers verify this signature against a public key in your DNS to confirm the email was not altered in transit.
How to set it up:
- Generate DKIM keys through your email provider.
- Add the provided CNAME or TXT records to your DNS.
- Enable DKIM signing in your email provider's settings.
Each email provider has its own process for generating and enabling DKIM. Follow your provider's documentation.
DMARC (Domain-based Message Authentication, Reporting and Conformance)
DMARC tells receiving servers what to do when an email fails SPF and DKIM checks, and where to send reports about authentication failures.
Start with a monitoring policy:
v=DMARC1; p=none; rua=mailto:dmarc@example.com
This tells servers to deliver all emails regardless of authentication results, but send aggregate reports to your specified address. Monitor these reports for a few weeks before tightening the policy.
Progress to a quarantine or reject policy:
v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com
Or:
v=DMARC1; p=reject; rua=mailto:dmarc@example.com
For more on authentication, see SPF, DKIM and DMARC Explained.
Step 4: Warm Up Your Mailboxes
A new mailbox that suddenly sends 100 cold emails looks suspicious to ISPs. Warm-up builds sending reputation gradually.
What warm-up does
Warm-up services send and receive emails automatically between your new mailbox and a network of other mailboxes. These automated conversations create a pattern of normal email activity, building positive reputation signals:
- Emails being opened.
- Emails being replied to.
- Emails being moved from spam to inbox (teaching ISPs that your messages are wanted).
Warm-up timeline
- Week 1-2: 10-20 warm-up emails per day. No cold outreach yet.
- Week 3-4: 20-40 warm-up emails per day. Begin cold outreach at very low volume (5-10 per day per mailbox).
- Week 5+: Continue warm-up alongside cold outreach. Gradually increase cold volume.
Warm-up tools
Many cold email platforms include built-in warm-up features. Standalone warm-up services also exist. The key features to look for: gradual ramp-up, reply simulation, spam rescue (moving emails from spam to inbox) and inbox placement tracking.
For more detail, see Email Warm-Up Guide.
Step 5: Choose a Sending Platform
You need a platform to manage your cold email campaigns. This is separate from your email hosting.
Cold email platforms
These are purpose-built for cold outreach:
- Send sequences of emails with follow-ups.
- Rotate between multiple mailboxes and domains.
- Track opens, clicks and replies.
- Manage bounce handling and unsubscribes.
- Include warm-up features.
- Enforce daily sending limits per mailbox.
What to look for
- Mailbox rotation: Distributes sending across multiple mailboxes to stay under per-mailbox limits.
- Sending limits: Configurable limits per mailbox per day to avoid triggering spam filters.
- Bounce handling: Automatic detection and removal of bounced addresses.
- Unsubscribe management: Automatic processing of unsubscribe requests (required by CAN-SPAM).
- Reply detection: Stops the sequence when a prospect replies.
- A/B testing: Test subject lines and email content for better performance.
Step 6: Build and Verify Your List
Your infrastructure is only as good as the list you send to. A high bounce rate (over 2-3%) will damage the reputation you spent weeks building.
List building
Start with clear targeting. Use the methods described in How to Build a Prospect List and How to Find Decision-Maker Emails.
If you have contacts in documents, exports or files, process them through Email Extractor to pull out all email addresses.
List verification
Before sending, verify every address on your list. Use a dedicated verification service. See Best Email Verification Services.
Verification targets:
- Remove all invalid addresses.
- Flag catch-all domains for cautious sending.
- Remove disposable and role-based addresses.
- Aim for a verified valid rate above 95% before sending.
Step 7: Monitor and Maintain
Metrics to track
- Bounce rate: Keep under 2%. Above 3% is a warning sign. Above 5% means stop sending and clean your list.
- Spam complaint rate: Keep under 0.1%. Even a few complaints from Gmail users can damage your reputation.
- Open rate: Below 20% may indicate deliverability issues (your emails are going to spam).
- Reply rate: Your ultimate success metric for cold outreach.
Domain rotation
If one domain develops deliverability problems, pause it and shift volume to your other domains. This is why you start with multiple domains.
Ongoing warm-up
Continue warm-up even after you start sending cold emails. The warm-up activity provides a baseline of positive signals that balance out the cold outreach.
List hygiene
Clean your list continuously. Remove bounces immediately. Re-verify addresses every 3-6 months. See How to Clean an Email List.
Common Mistakes
Sending from your primary domain
Never send cold email from your main business domain. One spam complaint wave can affect your customer communications for weeks.
Skipping warm-up
Sending cold email from a brand-new, unwarmed mailbox almost guarantees spam folder placement.
Sending too many emails too fast
Ramping up too quickly triggers spam filters. Start small and increase gradually.
Not verifying your list
Even a small percentage of invalid addresses can push your bounce rate over the threshold that triggers ISP penalties.
Ignoring bounce handling
Continuing to send to addresses that bounced compounds the damage. Automate bounce removal.
