Email Warmup Guide for Recruitment Agencies: DNS to First Campaign in 28 Days

You have signed up for a new outreach platform, connected a fresh email inbox, and written a killer campaign. You press send. Within 48 hours, your emails are landing in spam folders, your domain reputation is tanked, and your first campaign is dead on arrival.

This happens to recruitment agencies every week. The fix is not complicated, but it requires patience: you need to warm up your sending domain before running any outbound campaign.

Why Warmup Matters

Email service providers (Gmail, Microsoft 365, Yahoo) assign a reputation score to every sending domain and IP address. A brand-new domain has no reputation, which means no trust. When a domain with no sending history suddenly sends 200 emails in a day, spam filters interpret this as suspicious behaviour and route messages to junk folders. According to Validity's 2025 Email Deliverability Benchmark, new domains that skip warmup have a 68% spam placement rate in their first 30 days, compared to 11% for domains that follow a structured warmup protocol.

Every email you send from a new domain is evaluated against your sending reputation. A new domain has no reputation at all. Email providers treat this the same way a bank treats a new customer with no credit history: with suspicion.

The warmup process builds your domain's reputation gradually by sending small volumes of email to engaged recipients who open and reply. Over 14 to 28 days, this signals to email providers that your domain sends legitimate, wanted messages.

Step 1: DNS Configuration

Before sending a single email, your domain must have three DNS records correctly configured: SPF (Sender Policy Framework) authorises which servers can send on your domain's behalf, DKIM (DomainKeys Identified Mail) adds a cryptographic signature to each email proving it was not altered in transit, and DMARC (Domain-based Message Authentication, Reporting and Conformance) tells receiving servers what to do with emails that fail SPF or DKIM checks. Missing any of these three records will cause immediate deliverability problems regardless of content quality.

Three DNS records are essential before you send your first email:

SPF (Sender Policy Framework)

SPF tells receiving mail servers which IP addresses and services are authorised to send email from your domain. Add a TXT record to your domain's DNS:

v=spf1 include:_spf.google.com ~all (for Google Workspace)

v=spf1 include:spf.protection.outlook.com ~all (for Microsoft 365)

If you use multiple sending services (e.g. Google Workspace for email, a separate platform for campaigns), combine them in one SPF record. You can only have one SPF record per domain.

DKIM (DomainKeys Identified Mail)

DKIM adds a digital signature to every outgoing email, proving it came from your domain and was not tampered with. Both Google Workspace and Microsoft 365 provide DKIM keys that you add as CNAME or TXT records in your DNS.

DMARC (Domain-based Message Authentication)

DMARC tells receiving servers what to do when an email fails SPF or DKIM checks. Start with a monitoring-only policy:

v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com

After 2 to 4 weeks of monitoring (checking that legitimate emails pass), tighten to p=quarantine and eventually p=reject.

Step 2: The Warmup Schedule

Domain warmup follows a gradual volume increase over 14 to 28 days. Start by sending 5 emails per day in week 1, increase to 15 per day in week 2, 30 per day in week 3, and 50 per day in week 4. Each email should go to a real recipient who is likely to open and reply. Automated warmup networks accelerate this by simulating natural email activity across a pool of inboxes, generating opens, replies, and inbox-to-spam rescues that build domain reputation faster than manual warmup alone.

The goal is to gradually increase sending volume while maintaining high engagement rates:

The key metric is engagement rate, not volume. Email providers want to see that people who receive your emails open them, read them, and reply. A 50% open rate on 5 emails is vastly better for your reputation than a 5% open rate on 200 emails.

Step 3: Warmup Networks

A warmup network is a pool of email inboxes that automatically exchange emails with your sending domain. These inboxes open your emails, reply to them, mark them as important, and rescue any that land in spam folders. The network simulates natural email behaviour at scale, building domain reputation faster than manual warmup alone. According to a 2025 Lemwarm benchmark study, domains using automated warmup networks reach a stable sending reputation in 14 days on average, compared to 28 days for manual-only warmup.

Manual warmup works but is slow. Automated warmup networks accelerate the process by providing a pool of real inboxes that:

• Receive your warmup emails
• Open and read them (generating positive engagement signals)
• Reply with natural-sounding messages
• Move any emails from spam to inbox (the most powerful reputation signal)

Kolvera includes a built-in warmup network on the /mailboxes page. Once you connect your inbox, the warmup engine automatically pairs you with other inboxes in the network and begins exchanging emails using AI-generated content. The entire process is hands-off.

Step 4: Monitor and Adjust

During warmup, monitor three metrics daily: deliverability rate (percentage of emails reaching the inbox vs spam, target above 90%), bounce rate (should stay below 2%), and engagement rate (opens plus replies as a percentage of delivered, target above 40% during warmup). If deliverability drops below 85% at any point, reduce sending volume by 50% and investigate. Common causes of mid-warmup deliverability drops include sending to unverified email addresses, content that triggers spam filters, and SPF/DKIM misconfiguration.

Three metrics to watch during warmup:

• Inbox placement rate: Target above 90%. Below 85% means something is wrong.
• Bounce rate: Must stay below 2%. Higher rates signal bad data.
• Reply rate: During warmup, should be 30 to 50% (warmup network replies are counted).

If your deliverability drops mid-warmup, stop sending immediately. Common causes:

• Sending to unverified addresses (bounces kill reputation)
• Content with spam trigger words (FREE, URGENT, limited time)
• Broken DNS records (SPF/DKIM failures)
• Volume ramp too aggressive

Common Mistakes That Kill Deliverability

The five most common warmup mistakes for recruitment agencies are: starting campaigns before warmup is complete (day 1 sending to 200 prospects), using the same domain for marketing and outreach (reputation contamination), not verifying recipient email addresses before sending (bounces destroy new domain reputation), stopping warmup once campaigns begin (the warmup network should run continuously alongside campaigns), and using a free email address (gmail.com, outlook.com) for business outreach instead of a custom domain.

1. Sending cold campaigns on day 1. The single most destructive mistake. Your domain has zero reputation. Even 50 cold emails will trigger spam filters.
2. Using your primary domain for outreach. If your agency's website is yourcompany.com.au, do not send cold outreach from that domain. Use a dedicated outreach domain (e.g. mail.yourcompany.com.au or yourcompanyteam.com.au) so that any deliverability issues do not affect your primary domain's reputation.
3. Not verifying email addresses. Every bounce counts against your domain reputation. Verify every recipient email address before sending, especially during warmup when your reputation is fragile.
4. Stopping warmup when campaigns start. The warmup network should run continuously alongside your campaigns. The ongoing engagement signals from warmup emails counterbalance the lower engagement rates of cold outreach.
5. Ignoring DNS. If SPF, DKIM, or DMARC are not correctly configured, every email you send is fighting an uphill battle regardless of content or volume.

Frequently Asked Questions

How long does email warmup take before I can send campaigns?

A structured warmup takes 14 to 28 days depending on whether you use an automated warmup network (14 days) or manual warmup only (28 days). After warmup, start campaigns at low volume (15 to 20 emails per day per inbox) and scale gradually. Sending high-volume campaigns before warmup is complete is the most common cause of deliverability failure for recruitment agencies.

Can I warm up a Gmail or Microsoft 365 inbox?

Yes, both Gmail (Google Workspace) and Microsoft 365 inboxes can be warmed up. The DNS records (SPF, DKIM, DMARC) are configured through your domain registrar, not through Google or Microsoft. Google Workspace provides DKIM keys under Admin > Apps > Gmail > Authenticate Email. Microsoft 365 provides DKIM configuration under Exchange Admin Center > Protection > DKIM.

Should I use a separate domain for cold outreach?

Yes. Using a dedicated outreach domain (e.g. mail.yourcompany.com.au or yourcompanyteam.com.au) protects your primary domain's reputation from the inherently lower engagement rates of cold outreach. If your outreach domain's reputation is damaged, your primary website and business email remain unaffected. Set up the outreach domain with its own SPF, DKIM, and DMARC records and warm it up independently.