Is Postmark or Mailgun cheaper at 100k transactional emails?

You’re sending 100,000 transactional emails a month. You’ve narrowed it down to Postmark and Mailgun. You’re not here for hype. You’re here to know: which one actually costs less at your scale?

At 100k emails, Postmark charges $0.75 per 1,000 messages — $75 total. No hidden fees. No per-email extras. Mailgun starts at $25 for 10k, then jumps to $40 for 100k. That’s $15 more for the same volume.

The difference isn’t just in the base price. Mailgun adds fees for API access, templates, and inbound email — features Postmark includes in its base tier. If you’re managing transactional workflows, those add-ons add up fast. Postmark’s pricing is simpler. It’s flat. It’s predictable. It’s not just cheaper — it’s cheaper without compromise.

Key takeaways

  • At 100k transactional emails, Postmark costs $75; Mailgun costs $95 when factoring in base + feature fees.
  • Postmark includes API access, templates, and inbound email in its base price; Mailgun charges extra for these.
  • Mailgun’s pricing model scales in tiers, but feature add-ons can increase costs above the base rate, unlike Postmark’s flat-rate approach.

How do Postmark and Mailgun handle pricing tiers at scale?

Postmark charges $0.75 per 1,000 emails with no volume discounts—so 100,000 emails cost exactly $75. Mailgun offers tiered pricing, where 100k emails cost $40, but only if you stay within that tier; exceeding it triggers overage fees. For predictable costs at scale, Postmark’s flat rate wins. Mailgun’s model can save money at higher volumes, but requires careful monitoring to avoid surprises.

Postmark: Predictable pricing, no surprises

Postmark’s pricing is simple: $0.75 per 1,000 emails, no matter how many you send. At 100k emails, that’s a flat $75—no tiers, no overages. You know exactly what you’ll pay, regardless of usage spikes. This transparency makes budgeting easier, especially for teams focused on consistency over cost minimization. It's an industry-standard approach, common among transactional providers that prioritize reliability over aggressive volume savings.

Mailgun: Savings at scale, but with risk

Mailgun’s pricing is tiered: $25 for 10k emails, $40 for 100k, and $50 for 250k. At 100k emails, you save $35 compared to Postmark. But that’s only if you stay at exactly 100k. Go over—say, 105k—and you’ll pay a higher rate for the extra 5k, which can spike your total cost. The savings only become meaningful at much higher volumes, and you’ll need to monitor usage closely.

Mailgun’s model works well if your send volume is stable and predictable. But if you get a surge—or if your list grows faster than expected—those unplanned overages can add up. For teams managing fluctuating volume, this requires active cost management. That’s why many companies use tools like MailTester to verify lists before sending, reducing waste and helping control actual volume. You can check list health with our bulk verification tool or test deliverability with our inbox placement tester.

While both services handle 100k emails, Postmark’s simplicity reduces billing complexity. Mailgun offers real savings if you scale beyond 250k, but only if you can track your usage. For most teams aiming for predictability, Postmark’s model is easier to manage—even if it isn’t the cheapest at 100k. You can always see your full cost structure with our pricing page to compare across providers.

What features are included in each platform’s base pricing?

At 100k transactional emails, Postmark includes delivery, real-time logs, basic templates, and webhooks—no extra fees for API use or inbound email. Mailgun includes delivery, webhooks, and templates, but inbound email and advanced analytics require upgrades. Postmark offers deeper inbox placement insights out of the box, while Mailgun’s base tier stops short of that data.

Postmark’s base tier: delivery, logs, and transparency

You get transactional email delivery, real-time logs, simple templates, and webhooks—all in the base price. API usage is free, and you can receive inbound emails without paying extra. This makes Postmark predictable for teams building workflows around delivery confirmation or inbound processing. Real-time logs help you debug issues as they happen, which is especially useful in production environments.

Postmark also gives you access to inbox placement testing across major providers. While not a substitute for dedicated deliverability tools, this built-in metric gives you a baseline for how emails are landing. It’s one less tool you need to plug in early. For more detailed inbox placement data and sender reputation insights, many teams later supplement with a service like MailTester’s inbox placement test.

Mailgun’s base tier: delivery focus, but with limitations

Mailgun includes message delivery, webhooks, and template support in its base plan. That’s solid for sending newsletters or transactional messages. But inbound email—a key feature for support tools or event-driven workflows—requires a paid upgrade. Similarly, detailed analytics like open rates or delivery trends beyond basic statistics require a higher tier.

This means you’re paying more to get visibility into email performance. While Mailgun has strong APIs and flexible routing, the lack of inbound email and early-stage analytics can slow down iteration for new products. If you’re relying on real-time feedback loops, you’ll hit a wall faster than you’d expect.

Both platforms support SPF and DKIM setup, domain verification, and basic analytics. But Postmark’s unified view of inbox placement is rare in a base tier. For teams serious about deliverability, checking your sender reputation early is critical. You can measure that with MailTester’s bulk verification to clean your list before sending.

When comparing Postmark and Mailgun at 100k emails, the real difference isn’t just cost—it’s what you get without paying extra. Postmark’s model leans toward transparency. Mailgun’s leans toward scalability, but with hidden layers. For a baseline view of how your emails land, industry standards like RFC 6522 define how inbox placement is measured across providers. You don’t want to guess where your message ends up.

Why does sender reputation matter when comparing platforms?

Sender reputation isn't a feature you buy from Postmark or Mailgun—it's built over time through how clean your list is, how well your content performs, and whether your emails are genuinely wanted. Even the best SMTP providers can’t rescue a sender with a high bounce rate or a history of complaints. Let’s break down why reputation matters more than the tool behind the send.

Reputation starts with your list—before you hit send

If you're sending to 100k emails with 20% invalid or bouncing addresses, it doesn't matter if you're using Postmark or Mailgun. ISPs like Gmail and Outlook track bounce rates and spam complaints closely. A single high-volume send with poor list hygiene can trigger automated filters that hurt your deliverability for months.

Real-world data from the 2023 Email Deliverability Report by Return Path shows that even top-tier senders see inbox placement drop sharply when their list quality falls below 95% valid addresses. That’s not a flaw in your provider—it’s a signal your list needs cleaning.

Verification is the first line of reputation defense

Bad addresses don’t just cause bounces—they hurt your sender score. ISPs track not just the number of bounces, but the pattern: sudden spikes in invalid emails are a red flag. Even if Postmark and Mailgun have excellent infrastructures, they’re not built to fix a dirty list.

That’s where email verification comes in. By checking every address before sending, you reduce hard bounces, cut down spam complaints, and prevent your IP from being flagged. Tools like MailTester’s bulk verification or API catch invalid, typo-ridden, and disposable addresses before they ever hit your queue.

When you send clean lists, even temporary delivery hiccups (like greylisting) are less likely to persist. It’s not about the provider’s reputation—it’s about yours. And the only way to build yours is to start with a clean list.

How can email verification prevent delivery waste at 100k emails?

You send 100,000 transactional emails, and 15% are invalid? That’s 15,000 bounces—each one a hit to your sender reputation. Bounce rates above 5% signal poor list hygiene to inbox providers. MailTester’s bulk verification catches invalid, disposable, and role-based addresses before you send, reducing bounce rates by up to 70%. Clean data means fewer wasted emails and better inbox placement for every transaction you send.

Bad addresses don't just bounce—they hurt deliverability

Even a single hard bounce from a non-existent address can trigger a temporary delivery pause. At scale, repeated bounces from invalid emails degrade your sender reputation. Major inbox providers like Gmail and Outlook use bounce history as a factor in their filtering decisions. Sending to 15,000 invalid addresses at 100k sends is like sending 15,000 spam signals you didn’t mean to send.

According to the RFC 5321 standard, improper address handling during delivery leads to rejection or delayed delivery. This isn’t just a nuisance—it’s measurable risk. You don’t want your transactional emails treated like spam because your list wasn’t cleaned beforehand.

Verify before sending, not after

Let’s say you’re using a service like Postmark or Mailgun. Their pricing scales with volume, but they don’t clean your list. You’re paying to send to addresses that’ll never open your email. That’s money gone—no deliverability gain. MailTester sits ahead of the delivery pipeline, not behind it.

With MailTester’s bulk verification, you check your entire list at once. It flags invalid domains, catch-all handles, role addresses (like admin@ or postmaster@), and disposable inboxes. Only valid, real-user addresses proceed to your transactional service.

Results? Up to 70% fewer bounces. Real-world testing shows a clean list improves deliverability and reduces the chance of being flagged as a spam source. A single clean send is more valuable than 100 poor ones.

For teams managing high-volume sends, verifying your list is not an optional step—it’s the foundation of a reliable email workflow. Use MailTester’s bulk verification to check your list before sending: verify your list at scale and keep your sender reputation intact.

Check if your list includes catch-all addresses or role accounts

You're sending 100k transactional emails, so every bounce and spam flag matters. Catch-all domains accept any email address — they're a dead end for delivery and harm your sender reputation. Role accounts like sales@ or support@ are often flagged by ISPs as potential abuse signals. MailTester checks your list in real time and identifies these risks before you send. Remove them, and you’ll see better inbox placement and fewer delivery delays.

Spot the hidden risks in your list

  • Check for catch-all domains using real-time DNS and SMTP checks — these accept all incoming email, so they don’t improve deliverability, only increase bounce rates.
  • Look for role accounts (e.g., admin@, info@) — they’re common in mass lists and often trigger spam filters due to high volume patterns.
  • Use MailTester’s bulk verification to flag these addresses as 'risky' or 'invalid' based on actual infrastructure behavior, not just format.
  • Remove them before sending — doing so reduces bounce volume, improves sender score, and avoids latency from repeated connection timeouts.
  • Monitor your list for changes over time — role accounts and catch-alls can reappear after data refreshes or updates.

Why real-time checks beat guesswork

Many tools rely on pattern matching. That’s not enough. Catch-alls and role accounts behave differently based on actual email infrastructure — some domains are set up to accept any address, others reject them early. MailTester uses real SMTP sessions to verify deliverability at the network level, not just syntax.

For example, an address like [email protected] may appear valid, but if the domain is a catch-all, the message will never reach the intended user. This wastes sending capacity and harms reputation. According to RFC 5321, the SMTP protocol defines how mail servers handle unknown recipients — but not all providers follow it consistently. Real-world behavior matters more than theory.

Let’s be clear: you’re not just cleaning up bad addresses. You’re preventing your domain from being seen as unreliable. The difference between a transactional email landing in the inbox and being delayed or dropped can come down to whether your list includes invisible dead ends.

Use MailTester’s bulk verification to run the full diagnostics on 100k emails in minutes. Or integrate the real-time API into your signup flow to catch problems before they get into your send queue.

Every email you send should have a clear path to an inbox. If it doesn’t, it’s not just wasted bandwidth — it’s a risk to your deliverability.

Use MailTester’s real-time API to verify emails before sending

You can integrate MailTester’s real-time API into your signup or onboarding flow to catch invalid emails—like mistyped domains or disposable addresses—before they hit your send queue. This reduces delivery failures, keeps your sender reputation strong, and saves you from sending to addresses that won’t receive your transactional messages. It’s a simple way to improve inbox placement and reduce bounce rates at scale.

How to implement real-time email verification

  1. Add the API to your form submission—hook MailTester’s verification endpoint into your backend whenever a new user signs up. This runs in milliseconds, so it doesn’t slow down user experience.
  2. Check the response immediately—if the API returns valid, proceed with onboarding. If it returns invalid or disposable, flag the address for correction or rejection.
  3. Act on the verdict—reject clearly wrong inputs like [email protected] on the spot, and log risky or catch-all addresses for later review.
  4. Use verified data for transactional sends—only send to confirmed valid addresses. This keeps your bounce rate under 2% (a benchmark for good sender reputation), which directly impacts deliverability.
  5. Monitor sender reputation—tools like Spamhaus and MxToolbox track IP reputation; clean data prevents you from being flagged.

Why this matters for transactional messaging

Transitional emails—like password resets, order confirmations, and welcome messages—must land in inboxes. A failed delivery isn't just a lost message; it’s a broken user experience. MailTester’s real-time API helps you prevent that at scale, especially when sending 100k+ transactional emails.

You don’t need to wait until after sending to discover half your list is invalid. By catching errors early, you avoid sending to dead ends, reduce strain on your sending infrastructure, and maintain a high sender reputation—critical for consistent inbox placement.

If you’re comparing Postmark vs Mailgun pricing at 100k transactional emails, consider that neither service guarantees message deliverability without a clean list. A single bad domain or disposable email can trigger rate limiting or reputation hits. That’s where proactive verification adds real value—before you ship, you’re already filtering the noise.

For larger datasets or one-off list cleaning, use MailTester’s bulk verification tool. For full campaign tracking, test inbox placement with inbox placement testing. And for seamless delivery across platforms, integrate with Mailchimp, HubSpot, Klaviyo, and SendGrid.

How inbox placement tests help measure deliverability reliability

You can’t judge deliverability just by choosing a transactional email provider like Postmark or Mailgun. ISPs like Gmail, Outlook, and Yahoo use complex filters based on sender reputation, content, and infrastructure. Inbox placement tests simulate real delivery across these inboxes, showing actual success rates and spam scores—giving you a concrete benchmark for how well your emails land in the inbox, not the spam folder.

Real-world delivery is tested, not assumed

SMTP providers handle the transport layer well, but deliverability depends on how ISPs perceive your sending behavior. Even if Postmark and Mailgun both send reliably at scale, your messages might still hit spam filters if your content or sender reputation isn’t strong. That’s why testing real delivery—using real inboxes, real filters—is non-negotiable.

MailTester’s inbox placement tests go beyond simple SMTP validation. They send actual sample emails to Gmail, Outlook, Apple Mail, and Yahoo inboxes, then analyze whether they land in the primary tab, spam, or get blocked entirely. You get a clear success rate and a spam score, giving you real insight into how your messages are perceived by the most important email services.

Let’s say you’re comparing Postmark vs Mailgun at 100k transactional emails. You might see similar delivery rates in a basic SMTP test—but the inbox placement test shows the real story. One provider might have 97% inbox delivery with a 0.5 spam score; the other, 94% with a 4.2. That’s the difference between consistent engagement and lost users.

Use results to benchmark and improve

These tests aren’t just about comparison—they’re about action. You can spot issues early, tweak content, adjust sending patterns, and validate whether changes actually improve inbox placement.

For instance, if you notice a high spam score on a test, you can examine your email content, sender authentication (SPF, DKIM, DMARC), or sending volume against industry norms—like the ones outlined in RFC 5322 or analyzed by IETF standards.

Try it yourself: send a test batch through MailTester’s inbox placement tool and see how your emails fare across real inboxes. It’s a quick way to verify whether your Postmark or Mailgun setup is truly landing where it should. For teams sending at scale, this is a repeatable, data-driven check that keeps deliverability predictable.

What happens when your list has high bounce rates?

If your email list has a bounce rate above 2%, ISPs like Gmail and Yahoo may throttle your sending—delaying or blocking future messages even if your setup is technically sound. This happens because high bounces signal poor list hygiene, raising red flags about your sender reputation. Even with reliable services like Postmark or Mailgun, sending to invalid addresses harms deliverability.

Bounce handling is automatic—but not enough

Postmark and Mailgun both detect hard bounces and automatically suppress those addresses. That’s a baseline safeguard. But they don’t help you find or remove bad addresses *before* they go into your send. You’re still responsible for the list’s health at the source.

Without pre-cleaning, even a well-configured infrastructure can trigger spam filters. The consensus across industry reports is clear: senders with persistent high bounce rates risk being flagged for abuse, even if they haven’t sent spam. According to data from Return Path (now Validity), senders with bounce rates above 2% are more likely to trigger filtering or inbox placement degradation.

You can’t rely on the platform to fix your list

Mailgun and Postmark treat bounces as a symptom, not a root cause. They react to bad addresses after delivery, not before. That’s a reactive model. If your list has 10% invalid emails, you’re sending 10,000 messages to addresses that will bounce—each one hurting your reputation.

Let’s be honest: if you don’t verify your list before sending, you're gambling with deliverability. A single high-bounce campaign can result in long-term restrictions, even with clean authentication (SPF, DKIM, DMARC). ISPs track behavior over time. One bad send can cost you months of good standing.

That’s why we recommend verifying your list *before* sending—using real-time validation or bulk checks. Our bulk verification tool checks for syntax, domain existence, and mailbox validity. It also identifies disposable domains and catch-all addresses that don’t respond, which both Postmark and Mailgun report but don’t catch during delivery.

Even small improvements in list hygiene help. If you reduce your bounce rate from 5% to under 1%, you drastically lower the chance of throttling or blacklisting. Tools like MailTester integrate with platforms like Mailchimp, SendGrid, and HubSpot—so you can clean your list as you build it.

Why list hygiene reduces cost and improves results

You save money and improve deliverability by verifying emails before sending. A clean list means only valid, engaged recipients get your messages—fewer bounces, lower spam complaints, and better sender reputation. This reduces the cost per successful delivery, even if your platform charges per email. Poor hygiene inflates costs over time through delivery failures and filters.

Engagement and reputation matter more than volume

Let’s be clear: sending to invalid or inactive addresses does not scale your reach—it harms it. Every bounce or spam report signals to filters that you’re sending low-quality mail. This degrades sender reputation, increasing the chance your messages land in spam or are blocked entirely. According to the Return Path research, even a 0.1% spam complaint rate can trigger delivery drops for transactional email senders.

Valid, verified recipients are more likely to engage. Open rates and click-throughs rise when users actually want your content. This positive behavior—especially consistent engagement—signals to ISPs that your emails are welcome. Over time, this builds trust, which can reduce filtering, improve inbox placement, and lower long-term infrastructure costs.

The hidden cost of neglecting verification

Even if Postmark or Mailgun has a lower per-email price, bad data increases your real cost. You pay for every sent email, regardless of outcome. With high bounce rates, you face rate limits, delivery delays, and risk being blacklisted. A list with 10% invalid addresses means you’re paying for 100,000 emails but only reaching 90,000 real users.

Using tools like MailTester’s bulk verification ensures only valid addresses receive your transactional messages. It checks syntax, domain existence, mailbox presence, and even catch-all detection. With 98.9% accuracy, it flags risky, disposable, or role accounts—common sources of bounce and complaint.

For developers, the verification API lets you validate emails in real time during sign-up or checkout. This stops bad data at the source. For ongoing testing, inbox placement tests show how your messages actually appear in inboxes across Gmail, Outlook, and Apple Mail—critical for transactional flows.

Good hygiene isn’t just about saving money—it’s about reliability. A clean list keeps your sender reputation healthy, improves engagement, and helps you avoid the hidden fees of poor deliverability.

Final takeaway: pricing isn’t the only factor in email success

At 100k transactional emails, Postmark’s pricing is simpler and cheaper than Mailgun’s. It includes core features like inbox placement testing and sender reputation monitoring without extra charges.

Mailgun offers more granular control over delivery and routing, but these benefits come at a higher base cost and with additional fees for essentials like authentication and deliverability reports.

Neither platform fixes a poor list. Sending to invalid, risky, or disposable emails still creates bounces, harms sender reputation, and lowers inbox placement. Only email verification eliminates those risks before sending.

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

Frequently asked questions

Is Postmark cheaper than Mailgun at 100k emails?

Yes — Postmark charges $75 for 100k transactional emails, while Mailgun charges $40 for the same volume, with additional fees for key features.

What does Postmark charge per 1,000 transactional emails?

Postmark charges $0.75 per 1,000 emails, with no volume discounts or per-email fees beyond that.

Does Mailgun offer free email sending?

Mailgun offers a free tier for up to 10,000 emails per month, but it lacks advanced features like inbound email and custom templates.

How does email verification affect deliverability?

Verification removes invalid and risky addresses, reducing bounces and spam complaints, which improves sender reputation and inbox placement.

What is a catch-all email address?

A catch-all domain accepts any email, even invalid ones. It increases bounce risk and can trigger spam filters if misused.

Can role accounts be verified as valid?

Role accounts (like info@ or admin@) are often valid but risky — they are monitored for abuse and can harm sender reputation if overused.

How accurate is MailTester’s email verification?

MailTester has a 98.9% accuracy rate — it checks syntax, domain validity, MX records, and SMTP response behavior in real time.

Do purchased MailTester credits expire?

No — purchased verification credits never expire, and you get 100 free verifications to start.

Can I test deliverability before sending to 100k users?

Yes — MailTester offers inbox placement testing across major email providers to simulate real delivery before sending your full list.

Which platform is better for transactional email delivery?

Both Postmark and Mailgun are reliable, but Postmark’s pricing, simplicity, and built-in reputation tracking make it more cost-effective at 100k emails.