Why email deliverability fails even with good content

You craft a flawless campaign. The copy is sharp, the design is on-brand, and the timing is perfect. But your open rates are flat, and your inbox placement is slipping. Why? Because your list might be sending poison to your inbox.

Even the best content can’t overcome a list haunted by invalid addresses, syntax errors, or spam traps. Braze sends to every address it receives — including those that are wrong, outdated, or worse, deliberately set up to catch spammers. One bad address can trigger a bounce. Too many, and ISPs start flagging your sender IP.

Pre-send verification isn’t optional. It’s your first line of defense. Without it, you’re risking reputation, deliverability, and long-term access to inboxes.

Key takeaways

  • Email deliverability fails when invalid or risky addresses are sent to, even with perfect content.
  • Braze delivers to every address in your list, so poor list hygiene directly harms sender reputation.
  • Domain and syntax checks prevent bounces, reduce ISP red flags, and protect sender IP health.

What does a valid email address mean for Braze deliverability?

A valid email address for Braze deliverability means it passes syntax checks, confirms the domain exists with proper MX records, and verifies the mailbox actually accepts mail. Without all three, your message won’t reach the inbox—and could hurt your sender reputation. Let's break down why each step matters.

Syntax and domain-level checks happen before you send

Invalid syntax—like missing the @ symbol or using special characters not allowed—gets flagged instantly. You don’t need to send a message to find out an email is broken. These checks are built into email standards, defined in RFC 5322. Tools like MailTester catch them reliably before you hit send.

Domain-level validation ensures the email’s domain actually exists and has valid DNS records, especially MX records that point to mail servers. Sending to a domain without MX records or a DNS entry is pointless—it’s like mailing an envelope to a fictional street. MailTester’s domain check confirms the domain is live and ready to receive messages.

Mailbox existence is the final, critical hurdle

Just because a domain exists doesn’t mean the specific mailbox does. A catch-all domain might accept any address, but a real inbox must respond. That’s why verifying mailbox existence is the final gate. Without it, you risk bounces, spam complaints, and blocked emails.

Braze treats undeliverable messages as a signal that affects your overall sender reputation. High bounce rates or repeated failed deliveries can trigger filters, push you into spam folders, or even get you blocked by providers like Gmail and Outlook. A real-time verification step—like using the MailTester API—helps you catch these before the send.

For teams using Braze with large lists, tools like bulk email verification ensure every address meets all three criteria. You can also test inbox placement using MailTester’s inbox tester to simulate how your messages land in real inboxes.

Ultimately, valid doesn’t mean “formatted right”—it means deliverable. The goal is to avoid unnecessary sending, protect your reputation, and maximize inbox placement. That starts with verifying every address before it hits Braze.

How to test email deliverability in Braze with domain and syntax check

You can test email deliverability in Braze by validating addresses before ingestion using MailTester’s real-time API or bulk verification. This catches syntax errors, invalid domains, and risky addresses upfront, reducing bounces and protecting your sender reputation. Only sync verified 'valid' emails to Braze to ensure inbox placement and deliverability.

Step-by-step process to validate emails before Braze ingestion

  1. Run your email list through MailTester’s bulk verification tool to catch syntax issues and invalid domains before sending to Braze. This step identifies malformed addresses, non-existent domains, and catch-all setups early—reducing the risk of hard bounces and spam trap hits. Use the bulk verification feature for large datasets.
  2. Use MailTester’s real-time API to validate individual addresses at point of collection. Integrate the email verification API into your forms or onboarding workflows to block invalid or risky entries before they enter Braze.
  3. Connect MailTester to Braze via its native API connector to automate verification at ingestion. This pipeline ensures every new subscriber is checked against real-time deliverability rules—no manual filtering required. It’s one of the more reliable ways to maintain list hygiene without slowing down user acquisition.
  4. Review the verification verdicts: 'valid' means the address is deliverable and safe to send to; 'invalid' means syntax error or non-existent domain; 'catch-all' means the domain accepts all emails (risky due to high spam trap exposure); 'risky' indicates high bounce likelihood or potential spam trap status. Use the email verification API to fetch these results programmatically.
  5. Sync only 'valid' addresses into Braze. Letting 'catch-all' or 'risky' emails into your CRM or ESP is a common mistake that can trigger blacklisting. Tools like MailTester flag these so you can block them before they impact your sender reputation.

Why this matters for deliverability and sender reputation

Even a single high-risk email can hurt your reputation with inbox providers. According to RFC 5321, improper validation at delivery can result in temporary or permanent rejection. MailTester doesn't predict inbox placement but does catch almost all syntax and domain-level issues that would otherwise lead to delivery failure.

By pre-validating at the domain and syntax level, you reduce avoidable bounces by up to 30%—a meaningful improvement in deliverability. Tools like Braze rely on clean data to maintain trust with email providers. Keep your list lean and your reputation intact.

Start with 100 free verifications at MailTester’s pricing page, or test inbox placement directly with a real inbox test to see where your messages land before sending.

What each verification verdict really means

When you test email deliverability in Braze with domain and syntax check, each verdict tells you something concrete: Valid means the address is real and ready to receive mail, Invalid means it’s malformed or dead, Catch-all means the domain accepts all messages but likely leads to spam traps or bounces, and Risky flags addresses that may be role-based, disposable, or linked to spam patterns. These signals are critical for reducing hard bounces and protecting sender reputation.

Understanding the core verdicts

Let’s break down what each result actually means—not just what it says on the screen.

Verdict What It Means Delivery Risk Recommended Action
Valid The email syntax is correct, the domain resolves, and the mailbox accepts messages. It’s a working, active address. Low Safe to send to. No action needed.
Invalid Either the address has a syntax error (like missing @), the domain doesn’t exist, or the mail server permanently rejects it. High Remove immediately. Retrying these only harms your sender reputation.
Catch-all The domain accepts all emails, even invalid or fake ones. While this seems helpful, it's commonly abused by spammers and triggers filters. High High risk of bounce or spam filtering. Consider excluding, especially if you're sending transactional messages.
Risky Often a role address (e.g., admin@, support@), a disposable email address (like mailinator.com), or one tied to spam patterns. Medium to High Best to avoid. These may not deliver or may trigger inbox placements checks negatively.

Why semantics matter in email verification

Verdicts aren’t just labels—they represent real technical behaviors. A catch-all domain, for example, doesn’t reject non-existent users, but that same behavior makes it a magnet for abuse. According to RFC 5321, a well-configured mail server should reject non-existent recipients, not accept them silently. Catch-alls bypass that.

Similarly, role addresses like billing@ or info@ are often monitored or automatically discarded by mailbox providers. MailTester uses a combination of DNS, SMTP, and behavioral pattern detection to sort these out accurately—98.9% of the time. You can test your list before sending to Braze with bulk verification or use the real-time verification API for integration-level checks.

Even if an address passes syntax and domain checks, it can still fail inbox placement. That’s where inbox placement tests come in—because deliverability isn’t just about being valid. It’s about being trusted.

Why domain-level checks matter more than you think

You might think syntax is enough—after all, an email address looks valid. But a domain can pass a syntax check and still reject your message outright. That’s why domain-level checks are essential: they reveal whether a domain’s mail server is even willing to accept mail. No MX record? Blocked IP? Strict greylisting policy? Your email will fail silently, even if the address is perfectly formatted. MailTester checks these real-world barriers early—before you waste sends.

Finding the invisible barriers

Many bounces aren’t caused by invalid addresses—they’re caused by the domain’s configuration. A domain with no MX record won’t receive mail at all. Some domains block entire IP ranges or use greylisting, which delays delivery until the sender proves patience. Others enforce catch-all policies that accept all incoming mail but are often abused by spammers, leading to automatic rejection.

Even if an address passes syntax validation, it’s still subject to the domain’s inbound rules. A valid-looking address on a domain with rejected sender IPs still won’t reach the inbox.

Testing what matters: real-time SMTP validation

MailTester goes beyond syntax. It doesn’t just scan the address—it checks the domain's actual mail infrastructure: MX records, SPF, DKIM, and more. Then it simulates a real SMTP connection to the mail server to test whether delivery is possible at this moment.

This gives you a live view of deliverability readiness. It’s like sending a test email without sending one. You’ll know in seconds if a domain will accept mail now, regardless of syntax.

Real-time validation is especially useful in platforms like Braze, where large-scale sends depend on clean data. If your list includes 10,000 addresses, and 5% fail due to server-level rejections, those are wasted sends and potential harm to sender reputation.

With bulk verification or the API, you can test thousands of addresses quickly and identify problem domains before campaign launch. The system flags issues like missing MX records or strict greylisting policies so you can clean your list early.

Inbox placement testing takes it a step further—simulating actual inboxes and checking if your message ends up in the primary inbox or spam folder. It’s a full-stack check: syntax, domain health, and real delivery behavior.

It’s not just about avoiding hard bounces. It’s about preventing soft bounces, reputation damage, and poor inbox placement. SMTP standards define how mail should travel—MailTester validates those real-world rules, not just patterns.

Domain-level checks aren’t extra—they’re essential when you want your message to land where it matters.

How to automate domain and syntax check in your Braze workflow

You can automate domain and syntax checks by integrating MailTester’s API into your data ingestion or CRM sync process. This catches invalid emails before they hit Braze, reducing bounces, protecting sender reputation, and improving inbox placement. Let’s walk through the three core steps to build this into your flow.

Start with bulk verification before ingestion

  • Upload your email list to MailTester’s bulk verification tool to flag invalid, role-based, or disposable addresses.
  • Use the output to clean your list before pushing it to Braze via file upload or API.
  • This step prevents dirty data from ever entering your Braze campaign flow.

Embed real-time checks in your automation

  • Connect MailTester’s real-time verification API to your workflow engine—Zapier, Make, or similar.
  • Trigger a syntax and domain check on every new email entry during CRM sync or form submission.
  • Only pass valid addresses (with valid or risky status) to Braze, blocking invalid or catch-all domains early.
  • Set up a webhook in your CRM or marketing platform to send each email to MailTester before saving it.
  • Use the API response to route data—either push valid emails to Braze or flag invalid ones for review.

The domain and syntax check prevents emails from failing on basic rules. A valid syntax (e.g., [email protected]) isn’t enough—SMTP domain validation confirms the mailbox exists and accepts mail, which you’ll find is a common failure point in automated campaigns. RFC 5321 defines the technical expectations for email routing, and catching misformed or non-existent domains early reduces hard bounces and avoids IP reputation damage.

Automating verification before sending isn’t a luxury—it’s a foundation of sender reputation hygiene.

Integrating MailTester via API or webhook doesn’t require deep engineering. You can use the pre-built connectors or direct REST calls to validate millions of addresses with 98.9% accuracy. Credits never expire, so you can verify large lists over time without pressure. This approach scales safely with your growth and keeps your Braze inbox placement reliable.

When not to send to a 'valid' address

Just because an email passes syntax and domain checks doesn’t mean it’s worth sending to. Role-based addresses like admin@ or sales@ are often ignored or marked as spam. Disposable domains like mailinator.com validate technically but are unreliable for campaigns. Even a valid address can hurt your sender reputation if it leads to spam complaints. Use verification tools that detect these risks before you send.

Role accounts don't behave like real users

MailTester’s inbox placement testing shows that emails sent to role addresses like support@, info@, or sales@ often land in folders or get filtered out entirely. These addresses aren’t used for personal communication—they’re automated, monitored, or ignored. Sending to them inflates delivery rates artificially but does nothing for engagement.

According to industry data, role accounts are responsible for a disproportionately high number of spam complaints, even when the email content is clean. That’s because they often get shared across teams, monitored for spam triggers, or used for list harvesting. If a sender repeatedly contacts a role account, ISPs may flag the sender as high-risk.

Disposable domains break engagement

Domains like mailinator.com, temp-mail.org, or yopmail.com are valid at the DNS level and will accept messages, but they’re designed for short-term use. Any message sent there is likely to be discarded after minutes—or never read. Sending to them inflates your “success” rate, but zero recipients actually engage.

MailTester’s bulk verification service detects disposable domains and returns a "risky" status, so you can filter them out before sending. You can see how disposable domain checks work in real time with our bulk verification tool, which identifies such addresses with high precision.

High-risk addresses impact reputation

Even a technically valid address can harm your sender reputation if it's on a blacklisted domain or used by a spam trap. ISPs track complaint rates and engagement levels—sending to a high-risk address, especially a disposable or role-based one, can trigger filters or reduce inbox placement for future messages.

Using tools that go beyond basic syntax or MX checks helps you avoid these pitfalls. MailTester’s inbox placement tester simulates real delivery conditions, including how messages are handled by major providers like Gmail and Outlook. This gives you a clearer picture of whether your email will reach inboxes—or end up in junk folders.

How MailTester’s 98.9% accuracy improves Braze deliverability

You can significantly improve email deliverability in Braze by catching invalid, risky, or syntactically incorrect addresses before sending. With 98.9% accuracy, MailTester reduces false positives and negatives, ensuring you don’t block real users or miss bad ones. This precision keeps bounce rates low, improves inbox placement, and protects sender reputation with major ISPs and inbox providers.

Accuracy that matters: fewer false flags, fewer failed sends

High accuracy isn’t about hype—it’s about real-world impact. With 98.9% accuracy, MailTester cuts down on errors that would otherwise slip through. A false positive (a bad address flagged as valid) leads to bounces. A false negative (a good address marked invalid) means lost engagement. Both hurt your sender reputation over time.

Let’s be clear: every bounce, even a soft one, is a signal to email providers like Gmail or Outlook. Systems like these monitor sending behavior. Too many bounces, even from a clean list, trigger scrutiny or filtering. That’s why verifying email syntax and domain validity upfront matters.

Stronger reputation, better inbox placement

When you send only validated addresses—those confirmed to be syntactically correct and hosted on real domains—you reduce the risk of spam complaints and delivery failures. This directly supports inbox placement. Major inbox providers use delivery patterns to assess sender trust. Consistent, clean sends signal reliability.

Tools like MailTester’s inbox placement tester go beyond basic checks. They simulate real inbox delivery across providers, helping you see how your Braze campaigns land—even before you send. This gives you insight into real-world performance, not just theoretical syntax.

By integrating MailTester’s real-time verification API or bulk verification with your Braze workflow, you eliminate risk before it hits the inbox. That means fewer wasted sends, better engagement, and fewer headaches with blacklists or throttling.

Industry-standard practices, like proper SPF, DKIM, and DMARC alignment, don’t just protect your domain—they also reinforce trust with receivers. While not directly managed by MailTester, verification complements those policies by ensuring only deliverable addresses are ever sent.

The result? A sender reputation that’s not just clean, but actively strong. And that’s what gets your messages seen.

Your first 100 verifications are free – start now

You can verify 100 email addresses for free right now with MailTester—no strings attached, no expiration on credits you buy later. Run a quick syntax and domain check on your Braze list today and uncover invalid, risky, or deliverability-prone addresses before they hurt your sender reputation. Every clean address improves inbox placement, especially when combined with proper email authentication.

How to get started in 3 steps

  • Go to MailTester’s bulk verification page and upload your Braze list (CSV or Excel).
  • Choose “domain and syntax check” to filter out malformed addresses and non-existent domains—basic but essential filtering that catches ~30% of invalid emails before sending.
  • Review the results: valid, invalid, catch-all, or risky addresses—then remove or suppress invalids in Braze to improve deliverability.

Why it works for Braze and your delivery rates

MailTester’s 98.9% accuracy comes from checking actual SMTP responses, not just patterns. This means you're not just filtering syntax errors—you’re uncovering real dead zones: blocked domains, role accounts, and disposable inboxes that get flagged by major providers like Gmail and Outlook.

For example, a RFC 6522 standard defines how SMTP servers should reject invalid recipients. MailTester mimics this behavior in real time using live mail servers to validate delivery potential.

  • Use the real-time verification API to validate new leads as they enter your database—preventing bad actors from slipping through your Braze onboarding flow.
  • Test inbox placement directly with MailTester's inbox tester—see if your Braze campaigns land in primary folders or get hidden in promotions or spam.
  • Move seamlessly between tools: MailTester integrates with Mailchimp, HubSpot, Klaviyo, and SendGrid—Braze integrations are actively in development.
  • Never lose your purchased credits: all credits expire only if unused, but you won’t lose them through inactivity—so build your list quality over time without rushing.

Braze deliverability is only as strong as your list quality

No amount of campaign design, personalization, or segment refinement can compensate for a list riddled with invalid or risky addresses. Even the most polished message won’t reach inboxes if it’s sent to email addresses that don’t exist, are blocked, or are associated with spam traps.

Pre-send verification—using domain and syntax checks—is not a nice-to-have. It’s a foundational requirement for consistent inbox placement. Without it, every send risks damaging sender reputation, triggering filters, or increasing hard bounce rates.

Investing in list hygiene before sending through Braze reduces bounces, improves engagement, and builds long-term deliverability performance. Clean lists mean more reliable results, fewer warnings from ISPs, and better return on marketing spend.

Keep reading

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

Frequently asked questions

Can I test email deliverability in Braze directly?

Braze does not include built-in email verification or deliverability testing. You must verify addresses before sending using an external tool like MailTester.

What happens if I send to a catch-all email address?

Catch-all domains accept all messages, often leading to high bounce rates and spam complaints. This damages your sender reputation and risks blacklisting.

Does syntax check include common typos?

Yes. MailTester validates format rules like correct @ placement, valid characters, and domain structure. Typos like 'gmail.com' instead of 'gmail.com' are caught.

How does MailTester check domains without sending emails?

It uses DNS queries (MX, SPF, DKIM) and SMTP simulation to assess domain response behavior without delivering a message.

Can I integrate MailTester with Braze?

While direct Braze integration is not yet available, you can use MailTester’s API to verify lists before importing them into Braze.

What makes a domain 'risky' in MailTester’s results?

Domains known for disposable emails, mass sign-ups, or spam trap use are flagged as risky, even if syntax and domain checks pass.

How many free verifications do I get with MailTester?

You get 100 free verifications to start, with no expiration on purchased credits.

Do disposable email domains affect sender reputation?

Yes. Sending to disposable domains increases bounce rates and can trigger spam filters. It's best to avoid these addresses entirely.

Why does a valid email still bounce in Braze?

Even valid addresses may bounce due to full inboxes, rate limiting, or greylisting. Verification reduces but doesn’t eliminate all bounces.

How often should I verify my Braze list?

Verify your list before any major campaign, and re-check every 60–90 days due to address churn and domain changes.

What’s the role of SPF and DKIM in deliverability?

SPF and DKIM are authentication protocols that verify sender legitimacy. While MailTester doesn't generate them, it checks their presence and validity.

Can I remove role addresses after verification?

Yes. Use MailTester’s verdicts to identify role accounts (e.g. info@, support@) and filter them out before sending in Braze.