Integrate Mailgun & SendGrid Bounce APIs

Why do your email lists still contain invalid addresses after using Mailgun and SendGrid?

You’re sending transactional emails through Mailgun and SendGrid—two of the most reliable platforms out there. Yet your bounce rate is still creeping up. Why?

Bounce reports from Mailgun and SendGrid tell you an address failed to receive mail. But they don’t tell you whether that address was ever valid. Or if it’s a role-based email like admin@ or support@. Or if it’s one of the hundreds of disposable domains that auto-delete after a few days.

You’re relying on reactive data—messages that already failed. But the real fix is proactive: validating your list before you send. That includes checking for catch-all domains, greylisting quirks, and invalid syntax early.

Key takeaways

Bounce reports from Mailgun and SendGrid only flag delivery failures, not validity or long-term usability.
Without prior verification, lists still include role-based addresses, disposable domains, and inactive accounts—even with reliable transactional platforms.
Integrating their bounce reconciliation APIs with a proactive validation layer prevents sender reputation damage and improves inbox placement.

What happens when you ignore bounces from Mailgun and SendGrid?

You risk damaging your sender reputation, triggering spam filters, and seeing inbox delivery rates drop — even if your emails are legitimate. Bounce data from Mailgun and SendGrid is not just a log; it's a real-time signal of list health. Ignoring it means allowing invalid or non-existent addresses to persist, which harms deliverability over time.

Spam filters detect patterns, not intent

Even if you’re not sending spam, repeatedly sending to invalid addresses raises red flags. Email providers like Gmail and Outlook track bounce patterns as part of their filtering logic. A high hard bounce rate — especially above 2% — signals poor list hygiene and can trigger automatic delivery throttling or rejection.

According to industry standards, consistent hard bounces are a top metric used by ISPs to assess sender trustworthiness. If your Mailgun or SendGrid bounce rate climbs, your messages may end up in bulk folders or get blocked entirely.

Reputation degrades silently

Sender reputation isn’t a single score; it’s a cumulative judgment based on historical behavior. Each unverified email that fails to deliver adds friction. Over time, these failures erode your deliverability — often without immediate notice.

Once reputation dips, it takes weeks, sometimes months, to recover. By then, your campaigns may already be underperforming. You might not see the problem until you’re suddenly blocked by a major inbox provider.

That’s why integrating bounce reconciliation from Mailgun and SendGrid isn’t just a technical step — it’s a hygiene necessity. It keeps your list clean by flagging dead or misconfigured addresses before they harm your sender profile. Real-time validation tools can help, but only if they’re actively fed with bounce data.

For teams using Mailgun or SendGrid, linking your bounce logs to a verification system ensures that invalid emails never re-enter your pipeline. You can check your list’s health with a bulk verification tool, or use an API for ongoing cleaning. These processes help maintain a positive sender reputation — and keep your messages where they should be: in the inbox.

Learn how to keep your list clean and your deliverability high with automated email list validation at bulk email list cleaning.

How to turn Mailgun and SendGrid bounces into a real-time list hygiene system

You can turn Mailgun and SendGrid bounce data into a proactive email list hygiene system by pulling bounce reports from both platforms’ APIs, validating each bounced address in real time using Email List Validation’s API, and automatically removing invalid, catch-all, or role-based emails before they impact your next campaign. This avoids wasted sends and protects your sender reputation.

Step 1: Pull bounce data from Mailgun and SendGrid APIs

Both Mailgun and SendGrid expose bounce data via their REST APIs. Configure webhooks or scheduled API calls to pull hard bounces, soft bounces, and invalid address responses—especially those flagged as “permanent” (e.g. 5xx SMTP errors).

Bounces are a standard signal of list decay. According to an RFC 3463 (which defines SMTP status codes), permanent failures like “550 User unknown” directly indicate invalid addresses. Ignoring these degrades deliverability over time.

Step 2: Validate each bounced address with Email List Validation’s real-time API

Use the real-time email verification API to check each address flagged as bounced.
For every response, map the validity flags: valid, invalid, catch-all, role-based, or risky.
Focus on addresses marked as invalid or catch-all—they’re not actionable for your audience.

Why this matters: A hard bounce doesn’t always mean the address is dead—some may be catch-all domains where every email passes SMTP validation but never reaches a real inbox. Using real-time verification separates real errors from false positives.

Step 3: Automate removal of poor-quality addresses

Tag any address that returns invalid, catch-all, or role-based as a cleanup candidate.
Integrate with your CRM or ESP (like Mailchimp or HubSpot) via the Email List Validation integrations to auto-remove these from future sends.
Set up a daily or post-campaign cleanup process to maintain a healthy list.

Role-based emails (like info@, sales@) are not ideal for individual outreach. They often don’t track engagement, and large sends to such addresses can signal spam behavior. The Spamhaus Project lists high volumes of role-based sends as red flags in reputation scoring.

True list hygiene isn’t about how many emails you sent. It’s about how many of them were actually valid and engaged.

The real difference between hard bounces and invalid addresses

Hard bounces don’t always mean an email address is invalid—just that delivery failed at the time. Some addresses bounce due to temporary issues like DNS misconfiguration, mailbox quotas, or third-party filtering. A single hard bounce isn’t proof the address was never valid. That’s why checking validity independently is crucial.

Not all hard bounces mean an address is dead

When an email fails to deliver, the bounce reason might just be temporary. For example, a mailbox might be full, a domain’s MX record might be misconfigured, or a recipient server might be applying rate limiting due to volume. These issues resolve over time, meaning a bounce now doesn’t guarantee the address won’t work later.

Plus, some servers return hard bounces for messages that don’t follow strict delivery rules—such as missing or invalid DKIM signatures—even if the address itself is valid. The email wasn’t delivered, but the inbox still exists. You can’t assume a bounce = permanent invalidity.

That’s where deep verification matters

Mailgun and SendGrid’s bounce reconciliation APIs help identify delivery failures—but they don’t tell you if the address was ever real. To know that, you need to verify the address independently. Email List Validation checks the full path: whether the domain resolves, accepts mail, and responds to actual verification attempts—going beyond SMTP error codes.

Our tool validates not just syntax but actual delivery readiness. It checks for catch-all setups, disposable domains, and role-based addresses that often appear in lists but never open emails. Unlike basic bounce logs, it flags risky addresses before they harm your sender reputation.

For example, a domain might have a catch-all policy that accepts all emails—so a bounce doesn’t mean the address is invalid, just that it wasn’t delivered. This can inflate bounce counts without being a real hygiene issue. You can reduce false negatives by using real-time verification with a service that validates domains and mail flow, not just error codes.

Use real-time email verification to catch these cases early. Or, clean your full list with bulk list validation before sending campaigns. This reduces bounce rates, improves inbox placement, and protects your sender reputation.

As the SMTP RFC notes, delivery failures should not be assumed as permanent invalidity—only verified with active checks.

How Email List Validation complements Mailgun and SendGrid bounce data

You can’t rely solely on Mailgun or SendGrid’s bounce data to maintain clean lists. Bounces only tell you what failed after sending—by then, you’ve already damaged sender reputation, wasted resources, and potentially hit spam traps. Email List Validation catches invalid, risky, and high-fault domains before the first email leaves your server, reducing hard bounces by up to 90% and preserving sender reputation. It finds problems bounces can’t—like catch-all domains, disposable emails, and role accounts—before they hurt deliverability.

Before the send: proactive cleanup

Use real-time email verification to filter out invalid addresses before you send. This stops dead leads and invalid domains from ever hitting Mailgun or SendGrid.
Identify catch-all domains that accept all incoming mail—even misspelled or fake addresses—because they can trigger spam traps and hurt your reputation. RFC 5321 defines SMTP behavior, but doesn’t account for malicious or lax domain policies.
Filter out disposable email addresses (like tempmail.org) and role-based emails (like admin@, sales@) that often fail delivery or get flagged by email providers.

What bounce data misses—and how validation fills the gap

Mailgun and SendGrid bounce reports only flag messages that failed to deliver *after* being sent. You lose time, cost, and reputation impact before you know the issue.
Catch-all domains are invisible to bounce APIs because every email appears to “deliver.” But they’re common spam trap vectors, and your sender reputation can degrade silently.
Role accounts and disposable domains often don’t bounce at all—they just don’t get opened. Yet they inflate your list size and dilute engagement metrics, hurting inbox placement.
Validation uses multiple checks—SMTP, syntax, domain hygiene, and pattern analysis—to detect risks that bounces can’t see. You get a full risk score, not just a delivery fail.

For teams using Mailgun or SendGrid, running pre-send validation is non-negotiable. It reduces waste, strengthens reputation, and protects against hidden threats. Clean your entire list with bulk verification and keep your sender reputation intact. Use the real-time API for automated, high-volume cleanup across workflows. Your inbox placement depends on it.

A real-world example: fixing a 12% bounce rate with proactive validation

One SaaS company sent a campaign to 50,000 emails via SendGrid and hit a 12% hard bounce rate—well above industry norms. Using Email List Validation, they verified all bounced addresses and found 42% were invalid, 28% were role-based (like admin@ or sales@), and 15% used disposable domains. After removing these, their bounce rate dropped below 3% and inbox placement improved by 14%.

Diagnosing the root causes

High bounce rates don’t just hurt deliverability—they poison sender reputation. A 12% bounce rate signals poor list hygiene, which can trigger filters at inbox providers. SendGrid’s bounce reconciliation API helped identify hard bounces, but it didn’t explain why those addresses existed in the first place. The real fix came from understanding the sources: outdated data, automated form captures, and role-based addresses that don’t respond.

Role-based emails like support@ or info@ are common in poor-quality lists. They’re often treated as “catch-all” by mail servers, so even if the address isn’t real, SendGrid may report it as deliverable. This leads to inflated engagement and degraded reputation. According to a 2020 Return Path study, role accounts and temporary emails are among the top contributors to poor inbox placement.

Putting validation to work

Before sending, the company used Email List Validation’s bulk verification to clean their list. The tool classified each address—flagging invalid, catch-all, disposable, and role-based entries. They removed all invalid and disposable emails outright. For role-based addresses, they created a separate segmentation workflow to assess relevance, instead of sending to them blindly.

After this cleanup, they reran the campaign. The hard bounce rate dropped from 12% to under 3%, and inbox placement rose by 14%. This wasn’t luck—clean data directly enabled better sender reputation and higher engagement. The same process now runs before every broadcast campaign.

Proactive email list hygiene isn’t optional. It’s foundational. You can't rely on bounce reconciliation alone. You need to know what’s on your list before you send. That’s why tools like Email List Validation—which integrate with SendGrid and Mailgun via API—don’t just report bounces, they prevent them. See how: clean bulk email lists at scale.

Key steps to integrate Email List Validation with SendGrid and Mailgun bounces

You can improve email list hygiene by pulling bounce records from SendGrid and Mailgun, filtering out hard bounces and transient errors, sending the cleaned list to Email List Validation’s real-time API in batches of 1,000, then using the results to tag or purge invalid addresses in your CRM. This reduces hard bounces, protects sender reputation, and improves inbox placement over time.

Extract and filter bounce data from your email platforms

Set up event tracking in SendGrid using Webhooks or the Bounce API to capture bounce events in real time. Similarly, enable event notifications in Mailgun to receive bounce events via their API. These platforms deliver structured payloads with metadata like recipient, status, and error codes.
Parse the incoming payloads to extract email addresses. Filter for hard_bounce, mailbox_not_found, or rejected status codes. Exclude temporary or transient errors like mailbox_full or rate_limited, which may resolve after a retry.
Validate the filtered list client-side: ensure email syntax is correct, and cross-check against DNS records to eliminate malformed or unreachable addresses before sending to verification. RFC 6522 outlines standard bounce classification, helping avoid over-filtering.

Verify and automate cleanup with Email List Validation

Send the filtered list through Email List Validation’s real-time API in batches of 1,000. This size balances speed and reliability—small enough to avoid timeouts, large enough to minimize API overhead.
Receive verdicts per email: valid (deliverable), invalid (syntax or DNS failure), catch-all (replies to any address), risky (high bounce rate or suspicious pattern), or role-based (e.g., admin@, sales@, support@).
Automate the response: use webhooks or a script to update your CRM, ESP, or email database. If the result is invalid, catch-all, or role-based, flag or remove the address. For risky, apply a suppress list or reduce send frequency.
Reconcile results weekly. Track the reduction in bounce rates—especially hard bounces—as a proxy for list health. A consistent drop indicates effective cleanup.

Consistent use of verified bounce data reduces sender reputation damage. Platforms like Spamhaus track bad senders, and high bounce rates can trigger blocklisting. Cleaning your list reduces risk and supports long-term deliverability.

How catch-all domains hurt your deliverability

You might think a mail server that accepts every email is a win, but catch-all domains actually damage your sender reputation. They allow spammers to send messages to non-existent addresses, which makes your campaigns look like bulk mail. Email filters detect this behavior and can block your messages before they reach inboxes, even if your list is clean.

What catch-all domains actually do

When a domain is set to catch-all, it accepts all incoming mail, no matter the user part of the email. That means an address like [email protected] gets delivered just like [email protected]. Spammers exploit this by sending to random combinations — and if they're hitting large numbers, systems flag the domain as high-risk.

Let’s say you’re sending to [email protected], which exists, but your campaign also includes [email protected], which doesn’t. Because the domain accepts all mail, your message gets delivered anyway. But email providers track delivery patterns and see that a lot of non-existent addresses are being sent to. That’s a red flag for spam behavior.

Major providers like Spamhaus and MXToolbox monitor how aggressively a domain receives mail to nonexistent recipients. If a domain shows consistent catch-all behavior, it can be linked to abuse, even if your specific messages are legitimate. Senders using such domains often face higher filter thresholds or reduced inbox placement — even if your content is perfectly clean.

Why validation is essential before sending

Without real-time filtering, you're sending to addresses that may not even exist — and worse, their domain may be a catch-all. This increases bounce rates and damages your sender reputation over time. Even a single bounce from a catch-all domain can be flagged as a delivery issue.

Tools that verify email addresses before sending help you avoid this trap. They check for syntax, domain validity, and whether the address is likely to respond. For example, our bulk email list cleaning service identifies invalid, risky, and catch-all cases before you send.

When you integrate with SendGrid or Mailgun, you also gain access to their bounce reconciliation APIs — but you can only trust those signals if your list is already validated. Otherwise, you’re cleaning with dirty data. The best outcomes come from filtering first, then syncing with delivery platforms to keep your sending behavior clean and trusted.

Role-based email addresses (e.g. sales@, info@) should not be in your marketing list

You shouldn’t send marketing emails to role-based addresses like sales@ or info@ because they’re rarely monitored, often ignored, and frequently trigger spam filters. These addresses don’t engage, which hurts your sender reputation, and they can lead to bounce rates that signal poor list hygiene. Tools like Email List Validation can identify these patterns and help you exclude them before sending.

Why role-based addresses hurt deliverability

Role accounts are typically shared across teams and not checked regularly. When you send to them, there’s no inbox engagement — no opens, no clicks, no replies. Over time, ISPs like Gmail and Outlook track these behaviors and flag your domain as “low engagement.” That directly impacts inbox placement.

Mailgun and SendGrid both flag repeated deliveries to unengaged addresses. If your list includes dozens of role-based emails, your reputation score drops faster than you think. This isn’t just theory — major deliverability reports from Return Path and MxToolbox confirm that low engagement is one of the top three reasons bulk emails end up in spam folders. Return Path’s research shows that domains with high bounce and no-open rates see inbox placement drops of 30–40% during active campaigns.

How to catch and handle role-based addresses

Let’s be honest: many teams still collect “info@” and “support@” for outreach, thinking they’re valid. They are technically valid — they exist — but they’re not suitable for marketing. These addresses often fall into the “risky” or “catch-all” category during verification, indicating low deliverability potential.

Email List Validation automatically detects these patterns using domain behavior, naming conventions, and known role account lists. It flags them during bulk verification and gives you real-time feedback on whether to include or exclude them. Using the bulk verification tool, you can clean your entire list in minutes and target only active, engaged addresses.

It’s not about removing a few emails. It’s about protecting your sender reputation. Your campaign success depends less on how many emails you send and more on how many actually land in inboxes. Role-based addresses don’t help — they hurt. Eliminate them early, and you’ll see more consistent delivery, better open rates, and fewer complaints.

You’re only as clean as your last list audit — here’s how to stay ahead

Run monthly bulk verifications on your entire list to catch invalid, dormant, or risky emails before they harm deliverability. Sync real-time validation with new signups to prevent bad data from entering your system. Then, reconcile bounces from Mailgun and SendGrid with verification results to spot patterns that reveal larger issues—like outdated data sources or poor signup hygiene. This closes the loop between data quality, sender reputation, and inbox placement.

Monthly bulk verification keeps your list in top shape

Use bulk email list cleaning to scan your full database every 30 days. This catches outdated addresses, typos, and role accounts you may have missed.
Verify all email addresses across your customer base, including inactive users and old leads. A list with 5% invalid addresses can trigger sender reputation flags with providers like Gmail and Outlook.
Compare results with past audits to track improvements. Over time, clean lists consistently reduce hard bounces and spam complaints—key metrics used by inbox providers to judge sender trustworthiness.

Real-time API integration stops bad data at the source

Embed the real-time email verification API into your sign-up forms or CRM syncs. Let it check every new email before it enters your system.
Act on the result: only accept valid addresses. Decline emails flagged as “catch-all” or “risky” in real time—many of those never receive mail, and they hurt deliverability.
Use this automated guardrail to maintain a consistent standard. Over time, your data quality will stabilize, reducing monthly cleanup efforts.

Now, track how Mailgun and SendGrid handle delivery failures. Hard bounces should align with invalid addresses in your validation log. When they don’t—when a valid email bounces due to greylisting, a server timeout, or a temporary block—you’ve found a delivery issue, not a data issue.

Spamhaus and RFC 5321 outline the technical standards for email delivery and blocking. When your bounce patterns mismatch validation results, it’s a signal that the delivery infrastructure is the problem, not your list.

Over several months, correlate bounce types (hard, soft, spam trap) with validation verdicts. If hard bounces persist on valid addresses or catch-all domains are dropping, it suggests misconfigured sending setups or sender reputation problems. Fix those before they hurt your deliverability.

Let’s be clear: no system is perfect. But by combining automated validation with active bounce analysis, you stay ahead of drift, decay, and technical hiccups that ruin inbox placement.

Start improving list hygiene today with 100 free verifications

Integrating Mailgun and SendGrid bounce reconciliation APIs with Email List Validation helps you identify invalid addresses before sending, reducing bounces and protecting sender reputation.

You get 100 free verifications to test the integration immediately. No time limit — credits never expire, so you can validate lists on your schedule, regardless of volume or frequency.

Use the real-time API and dashboard analytics to monitor inbox placement improvements and track your bounce rate decline over time. Actionable insights turn data into cleaner lists and better deliverability.

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

Frequently asked questions

Can Email List Validation verify emails from Mailgun and SendGrid bounce logs?

Yes. You can feed bounce data from either platform into Email List Validation’s real-time API for batch verification.

How accurate is Email List Validation’s verification?

The service maintains 98.9% accuracy, consistently identifying valid, invalid, catch-all, and risky addresses.

Do I need to code to integrate the API with Mailgun and SendGrid?

Basic integration requires minimal coding. Use webhooks or scheduled API calls to fetch bounce data and send to Email List Validation.

Can Email List Validation detect disposable email addresses?

Yes. It identifies known disposable domains and flags them as risky during real-time checks.

What is the difference between hard and soft bounces in SendGrid?

Hard bounces are permanent failures — the email address doesn’t exist. Soft bounces are temporary errors, like a full inbox.

How does Email List Validation improve sender reputation?

By removing invalid, disposable, and role-based addresses, it reduces bounce rates and avoids spam trap exposure.

Does Email List Validation work with HubSpot and Klaviyo?

Yes. It integrates with HubSpot, Klaviyo, Mailchimp, and SendGrid — all via API or direct sync.

What do 'catch-all' and 'risky' verdicts mean?

Catch-all means the domain accepts all emails — increasing spam risk. Risky means the address may be invalid, disposable, or role-based.

Can I verify a list before sending with SendGrid?

Yes. Use Email List Validation’s API to verify lists in advance, then import only valid addresses into SendGrid.

Are Email List Validation credits valid forever?

Yes. Once purchased, credits never expire — allowing you to use them at any time.

How often should I clean my email list using this method?

Monthly bulk validation is recommended. For high-volume senders, integrate real-time checks on new signups.

Can I compare Email List Validation with NeverBounce or ZeroBounce?

Yes. All three offer email verification, but Email List Validation provides direct integrations with major ESPs and higher accuracy claims.