Before you send a single email from a new domain, there is one step that many senders skip or rush through: setting up email authentication. Getting your authentication records in place before you begin domain warmup is not just a best practice; it is the foundation everything else builds on. Without it, even a perfectly planned warmup schedule can fall apart the moment your first messages hit the inbox.
This guide answers the most common questions about authentication records and domain warmup, so you can start your sending program on solid ground and protect your sender reputation from day one.
What is domain warmup and why does it matter?
Domain warmup is the process of gradually increasing your email sending volume from a new or previously inactive domain over a period of weeks. Internet service providers and mailbox providers use sending history to judge whether a domain is trustworthy, and a sudden spike in volume from an unknown domain triggers spam filters almost immediately.
The warmup process builds a positive reputation by demonstrating consistent, engaged sending behavior. You start with small volumes sent to your most engaged subscribers, then increase volume incrementally as positive signals accumulate. Mailbox providers observe open rates, click rates, complaint rates, and bounce rates to decide how to treat your messages. A well-executed warmup earns your domain the trust it needs to land reliably in the inbox rather than the spam folder.
What makes warmup matter even more today is that mailbox providers have raised their standards significantly. Reputation is now evaluated at the domain level, not just the IP level, which means your sending domain carries long-term consequences for every campaign you run. Starting that reputation on a weak foundation makes recovery difficult and sometimes impossible without starting over entirely.
What are email authentication records and what do they do?
Email authentication records are DNS-based technical standards that prove a sending domain is legitimate and that the sender is authorized to use it. They give receiving mail servers a way to verify the sender’s identity before deciding whether to deliver, filter, or reject a message.
There are three core authentication protocols every sender needs to understand:
- SPF (Sender Policy Framework): A DNS TXT record that lists which mail servers are authorized to send email on behalf of your domain. Receiving servers check this record to confirm the sending IP is permitted.
- DKIM (DomainKeys Identified Mail): A cryptographic signature added to every outgoing email that allows the receiving server to verify that the message has not been altered in transit and that it genuinely originates from your domain.
- DMARC (Domain-based Message Authentication, Reporting, and Conformance): A policy record that tells receiving servers what to do when SPF or DKIM checks fail. It also enables reporting so you can monitor authentication activity across your domain.
Together, these three records create a chain of trust. SPF confirms the sending server, DKIM confirms message integrity, and DMARC ties both together with a policy and reporting layer. Without all three working in alignment, your domain is vulnerable to spoofing, phishing abuse, and poor deliverability outcomes.
Which authentication records do you need before starting warmup?
Before sending your first warmup email, you need SPF, DKIM, and DMARC published and verified in your DNS. These are non-negotiable prerequisites. Starting warmup without them means your messages may fail authentication checks and be rejected or filtered before you can build any reputation at all.
SPF record
Your SPF record should list every sending source authorized to send on behalf of your domain. This includes your email service provider, any transactional email platform, and any third-party tool that sends on your behalf. A common mistake is publishing an SPF record that covers only one sending source and forgetting others, which causes authentication failures for legitimate mail.
DKIM record
Your email service provider will generate a DKIM key pair and give you a public key to publish as a DNS TXT record under a specific selector. Once published, every outgoing message is signed with the corresponding private key. Make sure DKIM is enabled and signing is active within your ESP before you begin warmup, not just published in DNS.
DMARC record
Start with a DMARC policy of p=none during warmup. This monitoring-only policy means no messages are rejected based on DMARC failures, but you begin receiving reports that show you how your authentication is performing across all sending sources. As your warmup progresses and your authentication is confirmed to be working correctly, you can move toward a stricter policy.
BIMI (optional but valuable)
Brand Indicators for Message Identification is not required before warmup, but it is worth noting as a next step. BIMI allows your brand logo to appear next to your messages in supported inboxes, and it requires a DMARC policy of at least p=quarantine to activate. It is something to work toward as your warmup matures.
What happens if you start warmup without authentication set up?
Starting domain warmup without authentication records in place causes immediate and lasting damage to your sender reputation. Mailbox providers that cannot verify your identity are far more likely to send your messages to spam, reject them outright, or flag your domain as suspicious from the very first send.
The problem compounds. Every message that lands in spam during warmup generates a negative signal that becomes part of your domain’s reputation history. Those early signals are weighted heavily because your domain has no positive history to offset them. Recovering from a reputation that was damaged in the first few weeks of warmup is significantly harder than building it correctly from the start.
There is also a security risk. Without DMARC in place, your domain is exposed to spoofing and phishing attacks. Bad actors can send fraudulent emails that appear to come from your domain, and there is no mechanism in place to detect or stop it. This can damage your brand reputation with recipients and harm deliverability even for authenticated messages you send later.
How do you verify that your authentication records are working correctly?
To verify your authentication records, use a combination of DNS lookup tools and test email analysis. Send a test message to a tool like Mail Tester or Google’s Admin Toolbox, which will inspect your message headers and confirm whether SPF, DKIM, and DMARC are passing correctly. You can also check your raw email headers directly to see the authentication results.
What to look for in authentication results
In the email headers, look for the Authentication-Results field. You want to see all three protocols marked as pass. An SPF pass confirms the sending IP is authorized. A DKIM pass confirms the signature is valid. A DMARC pass confirms that at least one of SPF or DKIM aligns with your From domain.
Using DMARC reports to monitor authentication
Once your DMARC record is live, you will start receiving aggregate reports from mailbox providers. These XML reports show you which sending sources are passing or failing authentication and whether any unauthorized sources are attempting to send on your behalf. Reading these reports regularly during warmup gives you early warning of any configuration issues before they escalate into deliverability problems.
Before you consider warmup underway, confirm that every sending source you plan to use is passing all three authentication checks. A single misconfigured source can create inconsistent results that undermine the reputation you are working to build.
How Email Industries helps with domain warmup
At Email Industries, we work with senders every day who are preparing for a new domain launch or recovering from a warmup that went wrong. We understand how much depends on getting the technical foundation right before the first message goes out. Here is how we help:
- Auditing your existing DNS records to identify gaps, conflicts, or misconfigurations in SPF, DKIM, and DMARC before warmup begins
- Setting up and validating authentication records across all your sending sources so every message passes authentication from day one
- Building a customized warmup schedule based on your list quality, sending volume, and industry
- Monitoring DMARC reports and deliverability signals throughout the warmup period to catch issues early
- Using our Alfred platform to validate your list and remove problematic addresses before they damage your reputation during warmup
Whether you are migrating to a new ESP, launching a new sending domain, or rebuilding after a deliverability setback, we can guide you through the full process. Learn more about our approach on our Migrations and Warmups page, or contact us to talk through your specific situation with one of our deliverability experts.
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