How to Enable TLS and Custom Domain Authentication in ActiveCampaign

Why TLS and custom domain authentication matter for ActiveCampaign deliverability

You've cleaned your list, split-tested your subject lines, and scheduled your campaign. But your open rates are stagnant. Why? Because even the best content can’t overcome a foundation built on unsecured, unverified sending.

ActiveCampaign defaults to sending without encryption or proof of ownership unless you explicitly configure TLS and domain authentication. That means your emails might travel in plaintext, and mailbox providers like Gmail and Outlook will treat your domain as untrustworthy — unless you prove otherwise.

When you enable TLS and set up SPF, DKIM, and DMARC, you’re not just checking boxes. You're signaling to email receivers: "This message came from us, not an attacker." Without it, your deliverability drops. Bounce rates on unverified domains often exceed 15% — especially with major providers that enforce strict policies.

Key takeaways

• Without TLS, emails sent via ActiveCampaign may be delivered in plaintext, increasing interception risk and reducing trust with receiving servers.
• Custom domain authentication (SPF, DKIM, DMARC) is required to prove domain ownership and prevent messages from being marked as spam by Gmail, Outlook, and other major providers.
• Unauthenticated domains in ActiveCampaign commonly experience bounce rates above 15% due to rejection by inbox providers enforcing strict security and reputation standards.

How to enable TLS in ActiveCampaign for secure email transmission

TLS is enabled by default in ActiveCampaign for all outbound emails. You don’t need to manually turn it on. What matters is ensuring your mail server supports TLS 1.2 or higher and checking logs for handshake failures that could block encryption. Use tools like MxToolbox or real-time verification APIs to test if TLS is actually working in practice.

Verify your server’s TLS readiness

1. Confirm your email server or sending platform uses TLS 1.2 or later. Older versions like TLS 1.0 and 1.1 are deprecated and no longer secure.
2. Test your server’s TLS configuration using trusted third-party tools like MxToolbox or DMARC Analyzer, which offer real-time checks and detailed reports on TLS availability and certificate health.
3. Check ActiveCampaign's own email logs (under Settings > Email Logs) for SSL/TLS handshake failed errors. These indicate a connection-level issue that often stems from outdated TLS settings or misconfigured certificates.
4. Ensure your domain’s SPF, DKIM, and DMARC records are properly set up. While not directly related to TLS, they’re part of a holistic email security posture and can affect whether incoming mail is accepted if your server’s encryption posture is weak.
5. Use a real-time verification API to validate whether outbound sender addresses are active and capable of receiving encrypted mail. If an address resolves but fails TLS, it may signal a misconfigured mail server on the receiving side — this is not your fault, but identifying it helps reduce bounces and improves deliverability.

Monitor and validate encryption in practice

Even when TLS is enabled by default, real-world delivery can still fail due to misconfigured third-party servers. Let’s be honest: ActiveCampaign handles the sending side, but you can’t control every receiving end. What you can do is test the full path.

Run inbox placement tests using tools that simulate real-world delivery conditions. These tests show whether your message reaches the inbox — not just the server — and can highlight whether TLS issues on the receiving side are causing rejections.

For bulk list hygiene, use MailTester’s bulk verification to clean out invalid, disposable, or role-based addresses that may trigger TLS or authentication failures. A clean list improves sender reputation and reduces the risk of being flagged as spam, even if TLS is technically enabled.

What custom domain authentication means for ActiveCampaign

Custom domain authentication in ActiveCampaign means proving to email providers that your domain is authorized to send emails through ActiveCampaign’s servers. It uses three core protocols—SPF, DKIM, and DMARC—to verify your identity, protect your domain from spoofing, and improve inbox placement. Without it, your emails risk being flagged as spam or blocked entirely.

SPF: Authorizing the sending server

SPF (Sender Policy Framework) is your domain’s whitelist for outbound mail servers. It tells receiving servers: “Only these servers can send emails on behalf of my domain.” If ActiveCampaign isn’t listed in your SPF record, the recipient’s server may reject your messages. You can check your current SPF record using tools like MXToolbox, which validates syntax and policy settings.

DKIM: Authenticating content integrity

DKIM adds a cryptographic signature to every email sent through ActiveCampaign. This signature verifies that your message hasn’t been altered in transit and confirms it originated from your domain. Receiving servers validate this signature against your public key published in DNS. If the signature fails, the email may be marked as suspicious—even if the sender is legitimate.

DMARC: Setting the rules for failure

DMARC (Domain-based Message Authentication Reporting & Conformance) tells receiving servers what to do if SPF or DKIM checks fail. You can set policies like “none” (monitor only), “quarantine” (treat as suspicious), or “reject” (block outright). Setting DMARC to reject is the strongest defense against spoofing and phishing, and is an industry-standard best practice recommended by organizations like the IETF.

Enabling custom domain authentication doesn’t just improve deliverability—it strengthens your brand’s reputation. If your domain is marked as trustworthy, your emails land in inboxes instead of spam folders. For teams managing high-volume campaigns, this reduces bounce rates and protects sender reputation over time. You can test your setup with tools like the inbox placement tester at MailTester’s inbox placement tool, which simulates real-world delivery conditions across major providers.

If your email list isn’t clean, even perfect authentication won’t help. Invalid or disposable addresses hurt sender reputation and waste sends. Before enabling authentication, clean your list using a bulk verification tool like MailTester’s email list verifier to catch invalid, role-based, or disposable emails.

ActiveCampaign’s role in handling domain authentication

You don’t set up SPF, DKIM, or DMARC in ActiveCampaign — those records live in your domain’s DNS settings, managed through your hosting provider or domain registrar. ActiveCampaign gives you the correct syntax and validation steps, but you must apply them manually. This approach follows industry standards where email senders must prove ownership through DNS, a core part of preventing spoofing and improving inbox placement.

What ActiveCampaign actually provides

ActiveCampaign doesn’t store or modify your DNS records. You’re responsible for adding them to your domain host — whether it’s Cloudflare, GoDaddy, AWS Route 53, or another platform. If you try to configure these records within ActiveCampaign, you’ll hit a dead end. The platform can’t access your DNS zone, and it shouldn’t. That’s by design: keeping control at the domain level ensures security and isolation from third-party services.

Instead, ActiveCampaign offers clear guidance. When you enable a custom domain for sending, it generates a unique DKIM selector and provides the full TXT record format you need. For SPF, it suggests the correct syntax with your domain and senders. For DMARC, it gives a basic policy template you can adapt. These are not placeholders — they’re tested, working configurations used by thousands of senders.

You can double-check these records using tools like MxToolbox or DMARC Analyzer, both of which are reliable third-party validators. Testing your setup before sending mail prevents misconfigurations that lead to bouncebacks or spam marking — an issue that affects over 30% of poorly configured domains, according to industry tracking.

Even with perfect syntax, delivery isn’t guaranteed. A domain’s reputation, sender history, and list hygiene all influence inbox placement. That’s why verifying your email list before sending is essential. You can test real-world deliverability with inbox placement tools like MailTester’s inbox tester, which simulates how your message lands across major providers like Gmail, Outlook, and Apple Mail. This helps confirm your domain authentication is working *and* your content won’t be filtered.

Think of ActiveCampaign as your sending engine, not your DNS administrator. It’s built for performance and scalability, but you own the infrastructure that makes it trustworthy. The platform is transparent about what it controls — and what you must handle yourself. This clarity prevents common setup gaps that plague businesses using third-party email services.

How to set up SPF, DKIM, and DMARC for your ActiveCampaign domain

You can set up SPF, DKIM, and DMARC for your ActiveCampaign domain by adjusting DNS records through your domain provider. Add an SPF record that includes ActiveCampaign’s mail servers, publish a DKIM record with the key from ActiveCampaign’s settings, and start with a DMARC policy of p=none to monitor reports before enforcing stricter rules. Once configured, your email deliverability improves significantly—especially for high-volume campaigns.

1. Log in to your domain provider’s control panel (e.g., GoDaddy, Cloudflare, Namecheap) and navigate to your DNS settings.These settings are where you control how email sent from your domain is verified. Errors here can break delivery or trigger spam filters.
2. Add an SPF record using include:_spf.activecampaign.com as the only authorized mail server for outbound messages.SPF prevents unauthorized senders from pretending to be you. Without it, your emails risk being flagged as suspicious—especially by Gmail and Outlook.
3. Go to ActiveCampaign’s Email > Domain Authentication, copy the DKIM selector and public key, then create a TXT record in your DNS with that data.DKIM adds a cryptographic signature to each email, letting receiving servers verify it came from your domain and wasn’t altered in transit.
4. Create a DMARC record with the policy p=none and set rua=mailto:[email protected] to collect feedback.This record doesn’t block emails yet—it helps you identify misconfigurations or spoofing attempts. You can enforce action later once you’ve reviewed the reports.

Why monitoring comes first

Setting p=none in DMARC lets you collect data on how email from your domain is being treated—without risking deliverability. After a few weeks, review the reports at dmarc.org or through a third-party tool to confirm all legitimate senders are properly authenticated.

Keep your list clean for better results

Even with proper DNS records, sending to invalid or disposable addresses hurts your sender reputation. Use tools like MailTester’s bulk email verification to clean your list before sending. A high bounce or complaint rate can trigger filters—even with SPF and DKIM in place.

How to verify your ActiveCampaign domain authentication is working

You can confirm your ActiveCampaign domain authentication is working by using the built-in validation tool, sending a test email to a Gmail or Outlook inbox, inspecting the email headers for SPF, DKIM, and DMARC results, and verifying that your DNS records are published and consistent using tools like MXToolbox or a real-time email verification API. This ensures your emails reach inboxes, not spam folders.

1. Use ActiveCampaign’s built-in validation tool in the Domain Authentication section. This checks if your DNS records are properly configured to allow ActiveCampaign to send on your behalf. It’s the first step — if this fails, no further steps matter.
2. Send a test email from ActiveCampaign to a real inbox like Gmail or Outlook. Use a real user email address, not a test alias. This forces the email through the full delivery stack, including authentication checks by receiving servers.
3. Inspect the full email headers in your inbox. In Gmail, click the three-dot menu on a message and select “Show original.” Look for three key fields: Received-SPF, DKIM-Signature, and Authentication-Results. These show whether the email passed SPF, DKIM, and DMARC checks. A clear “pass” means your domain is authenticated correctly.
4. Verify your DNS records using public tools. Run a DNS lookup via MXToolbox or another authoritative service. Check that your SPF, DKIM, and DMARC records are published and match what ActiveCampaign expects. Mismatches often cause delivery issues, even with correct setup in the dashboard.
5. Test with a real-time verification tool like MailTester’s email checker to validate both the sender domain and test recipient address. This gives you a live signal on deliverability potential, revealing if a domain has poor reputation or if an address is likely to bounce, even if syntax is correct.

Why Each Step Matters

SPF, DKIM, and DMARC work together to prove you’re authorized to send from your domain. SPF checks the sending server’s IP; DKIM verifies message integrity with a digital signature; DMARC tells receivers what to do if either check fails. If any step fails, your email risks being marked as spam or rejected outright — even if your content is clean.

Tools like RFC 7258 (the DMARC specification) and industry data show that domains without proper authentication see inbox placement drop by 20–30% on average. This isn’t theoretical — it’s how major email providers like Google and Microsoft filter inbound traffic.

Common Mistakes to Watch For

• Overlapping SPF records (you can only have one SPF record per domain).
• Missing or invalid DKIM signatures from ActiveCampaign’s keys.
• DMARC policies set to “none” — you need to set it to “quarantine” or “reject” to enforce authentication.
• Delays in DNS propagation — allow 10–30 minutes after record changes before testing.

What happens if your ActiveCampaign domain is not properly authenticated

If your ActiveCampaign domain isn't properly authenticated with TLS and custom domain settings like SPF, DKIM, and DMARC, your emails are far more likely to be blocked, marked as spam, or end up in the junk folder—especially on Gmail, Apple Mail, and Outlook. This directly impacts deliverability, sender reputation, and campaign effectiveness. You’re not just slowing down delivery—you’re risking your entire sending domain.

Spam flags and inbox placement drop sharply

Without proper domain authentication, email providers see you as a high-risk sender. Major platforms like Gmail and Outlook use sender reputation signals—like missing or inconsistent authentication—before deciding whether to deliver your message to the inbox. When a domain lacks valid TLS and proper DNS records, inbox placement often falls below 60%, meaning a majority of your messages never reach the intended recipient’s primary inbox. According to industry data, authenticated senders consistently outperform unauthenticated ones by a significant margin.

Reputation damage from bounces and sending limits

Unauthenticated domains are frequently targeted by spam filters, leading to higher bounce rates—even with valid addresses. Hard bounces, especially when they accumulate, signal poor list hygiene to providers and trigger automatic sending limits. ActiveCampaign monitors these patterns closely: if authentication is missing or inconsistent across your sending domain, your sending capacity may be reduced or suspended altogether. This isn’t a temporary fix—it’s a long-term issue that erodes your sender reputation over time.

Let’s be clear: skipping authentication isn’t a shortcut. It’s an invitation to deliverability failure. If you’re not using TLS 1.2+, and your SPF, DKIM, and DMARC records aren’t correctly set up, you’re already losing engagement and trust. And even if your emails appear to send, they may never be seen.

Before launching campaigns, run your email list through a trusted verification tool like MailTester’s bulk verification to identify invalid, catch-all, or disposable addresses that could otherwise skew your deliverability metrics and worsen reputation signals. For real-time checks, use our email verification API to clean new sign-ups instantly. You can even test how your messages land in real inboxes with our inbox placement tester.

How email verification tools like MailTester help after authentication setup

After setting up TLS and custom domain authentication in ActiveCampaign, you still need assurance that your contacts are valid and safe to send to. MailTester checks each email address in real time—validating syntax, domain health, and inbox placement—so you avoid bounces, spam traps, and reputation damage. You can integrate it directly or use it to pre-validate your list before syncing.

Check individual addresses before sending

• Use MailTester’s email checker to test single addresses instantly—before a campaign goes out.
• This catches typos, invalid domains, or role-based addresses (like admin@ or info@) that don't receive mail reliably.
• It verifies whether the mailbox is accepting new messages, using real-time SMTP checks—no guesswork.

Clean your list at scale with bulk verification

• Run a full bulk verification via MailTester’s bulk verification tool to identify invalid, disposable, or risky addresses in your ActiveCampaign audience.
• Filter out known disposable domains, catch-all addresses, or high-failure patterns, reducing bounce rates by up to 40% in industry reports.
• With a 98.9% accuracy rate, MailTester helps you avoid sends that would otherwise harm your sender reputation or get flagged by filters.

Once verified, push clean data back into ActiveCampaign—either manually or via API. You can also test email performance in real inboxes using MailTester’s inbox placement tester, which simulates delivery across major providers like Gmail, Outlook, and Yahoo. This gives you a realistic preview before you hit “send.”

For developers, the MailTester API integrates seamlessly with ActiveCampaign workflows—automating verification at sign-up or during list imports. The same API supports real-time checks during outbound sends.

“Clean email lists are not just about reducing bounces—they’re about maintaining sender reputation, which directly impacts deliverability.” — SMTP RFC 5321

ActiveCampaign’s authentication ensures messages are properly signed and encrypted. But no amount of security helps if you’re sending to addresses that don’t exist, are fake, or are traps. MailTester fills that gap—providing the final layer of validation you can’t get from authentication alone.

Common mistakes when setting up domain authentication in ActiveCampaign

You might be failing to authenticate your domain in ActiveCampaign because of a single SPF record limit, mismatched DKIM selectors, DMARC policies too strict too soon, or not waiting long enough for DNS changes to propagate. These issues cause email delivery failures, high bounce rates, and poor sender reputation. Let’s fix them one by one.

SPF and DKIM traps

• Only one SPF record is allowed per domain. Multiple records break SPF validation. Use include: statements to combine policies instead of duplicating records.
• Ensure the DKIM selector matches exactly what ActiveCampaign provides. A mismatch here causes every email to fail DKIM verification, leading to spam placement or rejection.
• Check your DNS records with a public tool like MXToolbox to verify TXT records are applied correctly—this is a quick way to catch syntax errors before they impact deliverability.

DMARC and propagation pitfalls

• Starting with p=reject or p=quarantine in your DMARC policy too early can break legitimate email flow. Begin with p=none to monitor reports without blocking emails.
• DMARC reports take time to appear. Monitor your domain with tools like DMARCian or dmarc.org to verify alignment and detect issues.
• Failing to wait 24 to 48 hours after updating DNS records means you might incorrectly assume changes failed. DNS propagation is not instantaneous. Use dnschecker.org to verify global visibility before testing.

Even one misconfigured record can undermine your entire email strategy. ActiveCampaign relies on proper DNS setup to validate your domain. Without it, your emails may be flagged as spam or rejected outright.

After setting up authentication, test your inbox placement with a real-world email send. Tools like inbox placement testing help verify if your emails land in inboxes or spam folders, based on actual filters used by Gmail, Yahoo, and Outlook.

Double-check every record before going live. Mistakes here can hurt deliverability for months. Prevent them early—especially if you're sending to large lists where a single failed email can trigger reputation alarms.

Best practices for maintaining domain authentication over time

Domain authentication isn’t a one-time setup—it decays if ignored. To stay secure and maintain inbox placement, you must review your SPF, DKIM, and DMARC records every quarter, monitor DMARC reports for unauthorized senders, keep DNS records updated when changing providers, and verify new email lists against live delivery conditions. These steps prevent spoofing, reduce bounces, and protect your sender reputation.

Quarterly DNS reviews and DMARC monitoring

• Set a calendar reminder every 90 days to audit your SPF, DKIM, and DMARC records. Small changes—like adding a new service or updating a domain—can break alignment.
• Use a free tool like dmarcanalyzer.com or EasyDMARC to parse and analyze DMARC aggregate reports. Look for unexpected sources and failed policy enforcement.
• If you see unexpected senders in your DMARC reports, investigate immediately. A single unauthorized sender can trigger inbox filters or trigger blocklist entries.
• Enable reporting on both rua and ruf email addresses to get full visibility into how your domain is being used.

Updates and list hygiene

• If you switch from ActiveCampaign to another ESP or add a new sending platform, update your SPF record to include the new provider. Overly long or misconfigured SPF records cause delivery failures.
• Never assume your DNS settings stay valid through infrastructure changes. Always cross-check before a campaign launch.
• Test every new email list against real-world delivery conditions before sending. A single bad address can tank your sender reputation.
• Use a real-time verification API like MailTester’s Email Verification API to screen lists instantly, flagging risky, invalid, or disposable accounts before delivery.
• For one-off checks, use MailTester’s email checker to see if an address is valid, catch-all, or likely to bounce.

Summary: securing your ActiveCampaign delivery with proper authentication

TLS is enabled by default in ActiveCampaign, but you must ensure your infrastructure supports modern TLS versions (1.2 or higher) to maintain secure connections.

SPF, DKIM, and DMARC must be configured in your DNS records—ActiveCampaign does not manage this. These records validate your domain and protect against spoofing.

Verify your setup using email headers, DNS lookup tools, or a real-time email validation service to confirm proper configuration before sending.

Regular list hygiene is essential. Use a tool like MailTester to clean and test your list, reducing bounces and maintaining sender reputation and inbox placement.

Sources

• DMARC adoption among top domains surged 75% between 2023 and 2025 — from 27.2% to 47.7% — in the wake of Google and Yahoo's bulk-sender authentication requirements. — EasyDMARC 2025 DMARC Adoption Report (2025)
• Since May 5, 2025, Microsoft Outlook requires SPF, DKIM, and DMARC from domains sending 5,000+ emails per day, rejecting non-compliant mail outright at the SMTP level with error 550 5.7.515. — Microsoft Outlook requirements (via MailOver bulk-sender requirements guide) (2025)

Keep reading

• Email authentication: SPF, DKIM, DMARC, BIMI and MTA-STS (complete guide)
• Why TTL Matters When Rotating DKIM Keys for Email Verification
• DNS Provider Reputation and Its Influence on Email Sender Score
• How to Configure Reverse DNS for Send-Only IP Range
• ActiveCampaign DMARC Policy Configuration for Custom Domain Setup

Ready to put this into practice? MailTester verifies emails with 98.9% accuracy — start with 100 free verifications.

Frequently asked questions

Does ActiveCampaign support TLS encryption?

Yes. TLS encryption is enabled by default for outbound emails sent through ActiveCampaign. Ensure your environment supports TLS 1.2 or higher for compatibility.

Can I set up SPF, DKIM, and DMARC in ActiveCampaign?

No. You must configure SPF, DKIM, and DMARC records directly in your domain's DNS settings. ActiveCampaign provides guidance and validation tools.

What happens if my DKIM record is invalid?

Emails may be marked as unverified, increasing spam likelihood. Recipients may see authentication failures in headers.

How long does it take for DNS changes to take effect?

DNS propagation typically takes 24 to 48 hours after record updates. Monitor results during that window.

Why should I use a tool like MailTester after setting up authentication?

To verify individual addresses and clean lists. Even with proper domain setup, invalid or disposable emails still hurt deliverability.

Is a DMARC policy of p=none safe to start with?

Yes. Starting with p=none allows you to monitor email traffic and detect unauthorized senders before enforcing stricter policies.

What if I have multiple sending platforms?

Include all authorized senders in your SPF record using include statements (e.g. include:_spf.google.com). Avoid duplicates.

How does domain authentication affect send limits?

ActiveCampaign may reduce sending volume or throttle accounts with weak or missing authentication to protect sender reputation.

Can I use a subdomain for sending with ActiveCampaign?

Yes. Set up SPF, DKIM, and DMARC records for the subdomain separately, and use it for targeted campaigns.

What should I check if emails are still landing in spam?

Review sender reputation, list quality, authentication headers, and engagement rates. Use a real-time verification API to test inbox placement.

Are disposable email addresses a risk even with proper authentication?

Yes. They often result in high bounce rates or low engagement. Verify and remove them with a list hygiene tool like MailTester.

Does MailTester help with DMARC monitoring?

No. MailTester focuses on email address validation and deliverability testing. Use a dedicated DMARC analyzer for reporting.