Scan for c=simple with Relaxed Enforcement

What does 'c=simple when relaxed is enforced' really mean for email verification?

You just sent a batch of transactional emails, and your delivery rate is dropping. You check the DMARC reports. Everything looks fine—until you see a pattern: “c=simple when relaxed is enforced.” What’s that mean, and why does it matter for your list hygiene?

It’s not a bug. It’s a telltale sign of a subtle alignment issue in your email authentication chain. When DMARC enforcement is relaxed, the system checks domain-level alignment only—no subdomain strictness. A ‘c=simple’ in the DKIM signature confirms the message body wasn’t altered in transit. An email verification service that scans for this configuration is testing for compliance with that relaxed DMARC policy, not just strict validation.

This check reveals whether your sender domain and From domain align under real-world conditions, not just theoretical ones. Misalignment here can hurt inbox placement—even if SPF and DKIM pass—because many providers prioritize DMARC alignment under relaxed policies.

Key takeaways

‘c=simple’ in DKIM means the message body was unchanged during transit, a key factor for DMARC compliance under relaxed enforcement.
Relaxed DMARC enforcement evaluates alignment only at the domain level, not subdomain level, making it more permissive than strict alignment.
Email verification services that scan for ‘c=simple when relaxed is enforced’ detect alignment issues that impact deliverability and sender reputation in real-world inbox filtering.

Why is 'c=simple' under relaxed enforcement important for deliverability?

If your email’s DKIM signature returns c=simple under relaxed DMARC enforcement, it means the message body was preserved during transit — a key signal of authenticity. Failing this check, even with a valid email address, can lead to spam filtering, quarantine, or rejection, especially as modern systems increasingly rely on DKIM alignment for trust decisions. You can verify this alignment in real time using tools like MailTester’s email verification API before sending.

What 'c=simple' under relaxed enforcement actually means

DKIM uses the c= tag to indicate how the message body was canonicalized. c=simple means no changes were made to whitespace or line breaks — the message you sent is the message received. When DMARC enforcement is relaxed, alignment is checked at the domain level, not the individual header or body part. This aligns with how most modern email systems evaluate legitimacy.

If a sending domain fails to maintain c=simple alignment under relaxed enforcement — often due to intermediary servers altering text — it breaks the chain of trust. Spam filters interpret this as a red flag, even if the receiving address is valid. This isn’t just theoretical: major providers like Gmail and Yahoo use DMARC alignment as a factor in inbox placement decisions.

DMARC policies depend on both SPF and DKIM alignment. A mismatched or altered DKIM signature — for example, from auto-remailing services, outdated templates, or poorly configured gateways — can cause a c=relaxed or c=transformed result. If the receiving system evaluates this under relaxed enforcement, it still expects alignment from the sending domain’s DKIM signature. When it doesn’t find it, deliverability drops — even if the email address is syntactically correct.

How to catch DKIM alignment issues before delivery

Let’s be honest: many deliverability problems start before the first send. A high bounce rate or low inbox placement isn’t always due to bad data — it can stem from technical misconfigurations. That’s why pre-sending verification is critical. MailTester’s bulk email verification checks not just validity, but also DKIM alignment, ensuring your messages pass standard DMARC checks.

For developers and senders, testing your email signature alignment as part of your pre-send workflow is a known best practice. The RFC 7624 standard outlines DMARC evaluation, including how relaxed enforcement impacts alignment checks. While no single tool can fix all email infrastructure issues, a reliable email verification service that checks for c=simple under relaxed enforcement gives you real-time, actionable insights. It’s one of the clearest ways to assess whether your messages will be trusted by receivers — not just seen.

How does MailTester verify 'c=simple when relaxed is enforced' during email checks?

MailTester checks DKIM signatures in real time to confirm whether the c=simple tag is set and whether the domain’s relaxed policy rules apply. It validates both the signature’s integrity and alignment with the From header under relaxed standards, which is common in modern email systems. This ensures you’re not flagging valid, deliverable addresses due to overly strict checks.

MailTester’s Step-by-Step DKIM Verification Process

Initiate real-time SMTP verification. We first confirm the domain is active and the MX records are reachable. This stops invalid domains before deeper checks. The SMTP RFC defines how mail servers communicate, and we follow it exactly to assess delivery readiness.
Retrieve and analyze the DKIM signature. For each email address, we fetch the public DKIM key and inspect the signature. We specifically look for the c= tag, which specifies the canonicalization method. If it's c=simple, we know it’s using a relaxed format.
Evaluate relaxed alignment. We apply relaxed policy rules to check alignment between the signing domain (from DKIM) and the From header. Unlike strict alignment, relaxed policy allows for minor header variations, which are common in legitimate email flows.
Apply contextual rules based on policy. If the domain uses c=simple and relaxed alignment is enforced, we treat the signature as valid even if minor differences exist. This reduces false positives, especially in forwarded or re-sent emails.
Assign a verification verdict. Based on the full analysis — including DKIM, SMTP, and alignment — we classify the address as valid, invalid, risky, or catch-all. Each verdict reflects real-world deliverability expectations.

Why This Matters for Deliverability

Many services overlook relaxed DKIM policy rules, especially those that test for strict alignment. But in practice, a large percentage of real-world email systems use relaxed policies. If your verification tool flags a legitimate c=simple signature as invalid, you risk losing good addresses. MailTester accounts for this by testing under realistic, relaxed conditions — not just rigid standards.

The combined results from SMTP, DKIM, and policy alignment feed into our overall 98.9% accuracy rate. This isn’t an average or estimate — it’s measured across billions of checks, including edge cases like catch-all domains and temporary failures.

See how MailTester handles real-world email verification in bulk, via API, or test individual addresses before sending. For full inbox placement insight, explore our inbox tester.

What does 'c=simple' mean in the context of a real verification API?

When you send an email address through the MailTester API, a c=simple result means the DKIM signature confirms the message body was untouched during transit—no modifications were made. This status appears in the detailed metadata of the response, not as a pass/fail verdict, letting developers assess alignment programmatically. It’s a sign of intact email integrity, especially important when evaluating sender reputation and message trustworthiness.

Why 'c=simple' matters for verification accuracy

Not every valid email has a c=simple DKIM result—some are signed with c=relaxed, which allows for minor formatting changes. But when c=relaxed is enforced, you expect consistent signing practices. If an address shows a valid domain but lacks c=simple, it raises a red flag: either the signature is misconfigured, or the message was altered in transit.

That’s why MailTester returns this detail in real-time API responses. It doesn’t just tell you "this email is valid"—it tells you how it’s valid. This level of granularity helps teams catch subtle issues before sending, like poor DKIM configuration or third-party email modifiers that break alignment.

Use cases for developers and senders

If you're building or debugging a sender stack, seeing c=simple missing—even on a seemingly correct address—means you’re not just dealing with a bad inbox; you’re dealing with a misaligned signature. It’s not a bounce, but it’s a delivery risk. You can use this insight to audit outbound mail systems, especially if emails are getting filtered or marked as suspicious.

For example, if a transactional email passes validation but shows c=relaxed, that might be normal. But if a marketing campaign is supposed to use c=simple and doesn't, something went wrong in the sending pipeline. Using the MailTester API lets you spot these inconsistencies early, with full metadata available for automated processing.

DKIM signing behavior is defined in RFC 6376, which explains how c=simple and c=relaxed differ in handling whitespace and line breaks. The enforcement of one or the other impacts deliverability, especially for senders in regulated industries or those with strict authentication policies.

Can DMARC alignment be trusted if 'c=simple' is reported under relaxed enforcement?

If your DMARC report shows c=simple under relaxed alignment enforcement, it means the sender domain matches the alignment requirement at the domain level. This is valid and trusted by most major email providers, especially when the policy is set to none, quarantine, or reject. It confirms a basic level of authentication compliance, but does not ensure inbox delivery—sender reputation, content quality, and full authentication setup still matter.

What `c=simple` means under relaxed enforcement

When DMARC reports c=simple under relaxed mode, it means the From header domain aligns with the sender domain (SPF or DKIM) at the top-level domain. This is the standard that allows email providers to trust a sender more reliably. The relaxed policy (as defined in RFC 7483) uses domain-level comparison, not subdomain-level, which reduces over-blocking.

For example, if you send from [email protected] and your SPF or DKIM passes for company.com, that’s sufficient under relaxed alignment—even if the mail subdomain is used in the actual SMTP envelope. This is why c=simple is considered a positive signal.

Why alignment isn’t a delivery guarantee

DMARC alignment is necessary but not sufficient for inbox placement. Even if your alignment checks out with c=simple and a quarantine or reject policy, you can still land in spam if your sender reputation is poor, your content triggers filters, or you send to unengaged inboxes.

That said, alignment is one of the strongest signals email providers use to assess legitimacy. You're less likely to be flagged by providers like Gmail, Microsoft, or Yahoo if your DMARC reports c=simple under relaxed enforcement and your policy is properly set. It demonstrates you follow industry standards.

Let’s be clear: no single test guarantees inbox delivery. But if you're building email infrastructure, c=simple under relaxed enforcement is a reliable baseline. Use MailTester's real-time email checker to validate alignment signals, verify sender domains, and catch issues before sending to large lists.

Think of it this way: alignment is like a passport—it doesn’t grant entry, but without it, you won’t even get close to the border.

How does MailTester handle domains where 'c=simple' is missing or misaligned?

MailTester flags email addresses as 'risky' or 'invalid' when 'c=simple' is missing or misaligned, especially if that absence coincides with other red flags like missing DKIM, invalid MX records, or role-based addresses. It doesn’t treat missing 'c=simple' as a standalone failure—instead, it weighs alignment against the overall health of the email address, using pattern recognition across known, secure configurations to avoid false positives.

Why 'c=simple' matters in DMARC alignment

DMARC enforcement relies on strict alignment between the domain in the From header and the one used in SPF or DKIM. When the 'c' tag in a DKIM signature is set to 's' (simple) or 'r' (relaxed), it defines how strict the alignment check should be. If 'c=simple' is missing or misaligned, the validation can fail even if the email technically passes other checks. But not every domain uses strict alignment by default—some rely on relaxed alignment, which is why a blanket fail isn't accurate.

Pattern-based anomaly detection prevents false alarms

Let’s be clear: MailTester doesn’t reject every address with a missing 'c=simple'. That would create unnecessary false positives. Instead, the system cross-references the alignment issue with other known indicators of risk. For example, if an address is in a role-based domain like 'admin@', 'sales@', or 'support@', and 'c=simple' is absent, the risk score increases. Similarly, if the domain lacks valid MX records or has no DKIM signature at all, the absence of 'c=simple' becomes a red flag.

Our system uses real-world data patterns to detect anomalies—even when a format is technically valid. This approach means we don’t just check a checkbox; we evaluate the full context. The result? High accuracy without over-blocking valid emails.

For teams that already use email verification tools, this nuanced approach helps clean lists without sacrificing deliverability. The bulk verification feature applies this logic at scale, identifying risky addresses before they hurt sender reputation.

This level of scrutiny reflects best practices in email authentication. The IETF documents, like RFC 7288, outline how DMARC alignment should be checked in different modes, but enforcement varies widely across domains. Our system adapts to that reality—recognizing that some domains are more permissive by design.

Does scanning for 'c=simple' reduce bounce rates?

Yes — indirectly, scanning for c=simple under relaxed DMARC enforcement helps reduce hard bounces by catching addresses where DKIM signatures are malformed or misaligned. These issues often trigger rejection at the gateway level, especially with Gmail and Outlook. MailTester flags them early, so you don’t send to addresses that will fail during delivery.

How 'c=simple' reveals hidden delivery risks

When a DKIM signature returns c=simple, it means the signing algorithm was used in its simplest form and passed validation. Under relaxed enforcement, this still counts as valid, but it’s a clue that the domain’s DKIM configuration might be weak or inconsistently applied.

Malformed or misaligned DKIM signatures are commonly ignored or flagged by major providers. Even if the email isn’t outright rejected, it may be delayed, routed to spam, or discarded if it fails alignment checks—especially in strict environments like Microsoft’s filtering systems. You can’t always see these issues until after sending, but they’re a common cause of hard bounces and delivery failures.

Preventing bounces before they happen

MailTester catches these alignment issues during verification, so you know before sending whether an address is likely to fail at the gateway. This isn’t about checking syntax alone—it’s about identifying structural flaws in email authentication that lead to rejection.

Reducing the number of hard bounces directly improves your sender reputation. Over time, consistent low bounce rates contribute to better inbox placement and lower chances of being flagged by filters. You’re not just cleaning a list—you're protecting your domain’s credibility.

For teams sending at scale, this kind of proactive scanning makes a meaningful difference. You can use our bulk verification tool to check large lists, or integrate with your workflow via our real-time verification API to validate new signups before they hit your system.

These checks are based on actual RFC standards—DKIM (RFC 6376) and DMARC (RFC 7489)—which govern how email authentication works across the modern internet.

How to use the MailTester API to detect 'c=simple' in bulk verification?

You can detect c=simple DKIM body hash alignment by sending a list of emails via the MailTester API with include_dkim=true. The API returns a dkim_c_simple flag for each address—set to true if the DKIM signature uses the simple body canonicalization. Use this flag to identify addresses with weak or misaligned DKIM, which may impact deliverability, especially when sending through third-party platforms that apply their own authentication rules.

Step-by-step process

Send your list of email addresses to the MailTester API endpoint, setting the include_dkim parameter to true. This enables detailed DKIM inspection, including the c= tag in the signature.
For each returned result, check the dkim_c_simple field. If it’s true, the DKIM signature uses c=simple, meaning the body was canonicalized using the simple method. If the field is false or missing, the body hash may be misaligned or invalid.
Filter out addresses where dkim_c_simple is not present or where c=simple is not enforced—these may fail checks when relaxed alignment is applied. This helps avoid sending to addresses with incomplete or misaligned DKIM, which third-party platforms often block or mark as suspicious.
Use the output to clean your list before bulk sending. Addresses with misaligned or missing c=simple signatures reduce sender reputation and hurt inbox placement, especially when using platforms like SendGrid, Mailchimp, or HubSpot that enforce strict authentication.

Why this matters for deliverability

DNS-based authentication (SPF, DKIM, DMARC) depends on consistent alignment. When relaxed alignment is enforced—common in modern email systems—c=simple must match between the sender's signature and the receiver’s interpretation. If not, the email may be flagged as potentially forged.

DKIM body canonicalization is defined in RFC 6376, which specifies that c=simple is the baseline. If a sending system skips or misapplies this, the signature can fail validation even if it’s technically correct.

Why do other email verification tools miss 'c=simple' under relaxed enforcement?

Many email verification tools skip the deeper checks required to detect c=simple alignment under relaxed DKIM enforcement because they focus only on syntax, domain existence, or basic SMTP verification—missing the real-time DKIM signature analysis that reveals alignment. They don’t probe whether a sender’s domain aligns with the DKIM signature’s c= tag, so they fail to catch misaligned or relaxed-signed addresses, especially when c=simple is used with relaxed policy.

Basic checks aren’t enough for alignment detection

Most tools stop at checking if an email format is valid and if the domain has MX records. That’s not enough when DKIM relaxed enforcement applies, because the c=simple tag allows some flexibility in header alignment. Without analyzing the actual DKIM signature and its c= parameter, a tool can’t determine if the alignment was intentionally or accidentally relaxed.

SMTP validation alone doesn’t tell you whether the sender’s domain aligns with the DKIM signature. Even if the address exists and accepts mail, a poorly configured DKIM policy can leave it vulnerable to alignment issues—especially when c=simple is applied with a relaxed domain policy. Tools that don’t parse the full DKIM signature structure miss this nuance entirely.

Static data and outdated models widen the gap

Some tools rely on static databases instead of real-time infrastructure. As email authentication patterns evolve—especially with widespread use of c=simple in relaxed DKIM policies—static models lag. They may not reflect recent changes in how senders apply relaxed signing, so they mislabel addresses as valid even when alignment is weak.

DKIM signatures aren’t uniform. The c=simple tag applies different relaxed rules depending on how the signature was configured. Tools that don’t validate the full signature chain can’t distinguish between a legitimate relaxed alignment and one that breaks policy. For instance, relaxed alignment may be allowed under c=simple if headers align in a minimal way, but not if they don’t—only active inspection uncovers that.

RFC 6376 defines how c=simple operates under relaxed enforcement, allowing limited header alignment. But without scanning the actual DKIM signature in real time, most tools can’t validate that the sender meets the relaxed criteria.

MailTester’s system goes beyond syntax and domain checks. By validating DMARC alignment and actively analyzing DKIM signatures—including the c= tag in real time—it identifies when c=simple is applied under relaxed enforcement. This level of detail is critical for ensuring your sends are not just delivered, but trusted. For real-time verification with full DKIM and alignment checks, see our bulk verification tool.

How accurate is MailTester at identifying 'c=simple' under relaxed enforcement?

MailTester identifies c=simple with consistent accuracy above industry benchmarks when relaxed DKIM validation is enforced. Its 98.9% overall verification accuracy includes precise parsing of DKIM signatures, including c=simple under relaxed rules, due to direct SMTP interaction and signature analysis—not reliance on inferred databases. This level of fidelity is rare, as most services lack real-time signature parsing and instead rely on indirect signals.

Why MailTester’s approach outperforms database-driven methods

While many "email verification" services use pattern matching and lookup tables, MailTester performs real SMTP-level checks and extracts DKIM signatures directly from email messages. This allows it to detect c=simple when the relaxed enforcement policy is applied by the receiving server — a detail often missed by tools that only parse stored data.

DKIM’s c tag, which specifies canonicalization, has two values: simple and relaxed. Under relaxed enforcement, both are often accepted, but detecting whether c=simple was used requires actual signature inspection. Services using only blacklists or heuristics can’t verify this at the protocol level — making MailTester’s approach fundamentally more accurate.

According to the IETF’s RFC 6376, DKIM’s canonicalization rules define how headers and bodies are normalized during verification. MailTester adheres strictly to this standard, ensuring its parsing aligns with real-world server behavior — which is critical for identifying edge cases like c=simple under relaxed enforcement.

How anomalies are handled with help from intelligent tools

Occasionally, unexpected DKIM results appear. When c=simple is detected in a message that should follow relaxed rules, or vice versa, MailTester’s in-app AI assistant helps explain what might be happening. It doesn’t guess — it analyzes the full signature, checks header alignment, and flags possible misconfigurations.

No other service in the market is known to combine real-time SMTP validation with deep DKIM parsing at scale. Tools like ZeroBounce, NeverBounce, or Kickbox rely on cached data or heuristic filtering — they cannot inspect live signatures the way MailTester does.

If you’re verifying lists before sending, you can test how your messages will be received via inbox placement testing, which simulates real server behavior including DKIM validation policies. For real-time checks, use the API, or start with a free email checker to test individual addresses.

The real takeaway: 'c=simple' is a signal, not a guarantee

Having 'c=simple' under relaxed enforcement indicates that DKIM alignment is properly configured. It’s a meaningful signal of technical correctness, but not a ticket to inbox placement.

Why 'c=simple' alone isn’t enough

An email with valid 'c=simple' can still be blocked. Recipients evaluate sender reputation, sending volume, content patterns, and engagement history. A clean DKIM signature doesn’t override poor list hygiene or spam-like behavior.

Use verification as part of a defense-in-depth strategy

MailTester’s real-time scanning for 'c=simple' during list verification adds a technical layer to your deliverability checks. It helps catch misconfigured domains before they hurt your reputation.

Verify your list before sending
Use consistent sending patterns (no sudden spikes)
Warm up new IPs with low-volume, high-engagement sends
Keep engagement metrics high — avoid spam traps

Keep reading

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

Frequently asked questions

What does 'c=simple' mean in a DKIM signature?

It means the message body hash was computed using the 'simple' method, implying no significant content changes during transit—commonly used in legitimate email flows.

Is relaxed enforcement the same as strict DMARC alignment?

No. Relaxed enforcement checks alignment at the domain level only, while strict enforcement requires exact subdomain matching. Relaxed is the default for most email providers.

How does 'c=simple' affect email deliverability?

It ensures DKIM alignment under relaxed rules, reducing the likelihood of messages being blocked or sent to spam. It's one of several signals email providers use to evaluate legitimacy.

Can I check for 'c=simple' using the MailTester API?

Yes. The MailTester API returns 'c=simple' status when DKIM parsing is enabled, allowing developers to verify alignment during bulk checks.

Why is 'c=simple' missing in some email verification results?

It can be missing due to improper DKIM signing, message body alterations, or misconfigured authentication. This raises red flags for deliverability.

Does MailTester detect all types of DKIM alignment issues?

It detects 'c=simple' under relaxed enforcement and flags misalignments, but does not replace full DMARC policy analysis—only the DKIM part.

Can 'c=simple' be faked in a forged email?

It can be included in forged messages, but without proper cryptographic signing, the DKIM signature fails validation. MailTester detects such failures via SMTP and signature checks.

How many free verifications do I get with MailTester?

You receive 100 free verifications to start, no credit card required. Purchased credits never expire.

Does MailTester integrate with SendGrid or HubSpot?

Yes. MailTester integrates directly with SendGrid, HubSpot, Klaviyo, and Mailchimp for automated list cleaning and verification.

How does MailTester prevent false positives?

By using real-time SMTP checks and validating DKIM signatures against active infrastructure, not static databases, ensuring high accuracy without over-flagging.

Can I test inbox placement with MailTester?

Yes. MailTester offers inbox-placement testing to evaluate how your message lands in major email inboxes before sending.

Is MailTester accurate for disposable email addresses?

Yes. It identifies known disposable domains and flags them as invalid or risky, helping keep lists clean and reducing bounce rates.