Picking an email provider is not just a branding choice. It is an engineering decision that affects how you send email (API or SMTP), how you monitor delivery (logs and events), and how quickly your team can debug “email not received” tickets.
This comparison is written for SaaS and development teams sending transactional messages such as password resets, OTPs, invoices, and account alerts. It focuses on practical tradeoffs: what features are required before production (webhooks, suppression management, logs), what stack patterns each provider usually fits, and what commonly goes wrong during migrations.
You will also get a technical decision flow and a migration checklist you can use in a review. There are no inbox placement guarantees here because mailbox providers decide placement, but the right provider setup makes incidents easier to diagnose and reduces avoidable risk.
If you are planning your own transactional email setup, use the MailCub Documentation to validate API fields, authentication, and event tracking requirements, and review the Transactional Email Service for a production-focused email workflow.
Quick Answer
- Choose Postmark if you are primarily transactional and want clean separation for different message types (for example, transactional vs bulk/broadcast).
- Choose Mailgun if you want a flexible email platform with stronger “email ops” controls around events, routing, and domain-level configuration.
- Choose SendGrid if you want broad ecosystem adoption with both Email API and SMTP options and a large feature surface.
- In all cases, require webhooks/events, logs/analytics, and suppression management before production cutover.
- Dedicated IPs are a tradeoff. Use them only when your volume, process, and monitoring justify the added operational responsibility.
Why It Matters
Transactional email is part of product functionality. If password resets or OTPs fail, users churn and support costs increase.
Your provider choice directly affects incident response. With strong logs and webhook events, your team can quickly confirm whether a message was accepted, deferred, bounced, blocked, or delivered. Without that visibility, debugging turns into guesswork.
It also affects long-term reputation risk. If transactional and bulk traffic are mixed without clear separation, deliverability can become unstable in ways that are hard to explain to customers.
Postmark vs Mailgun vs SendGrid: Quick Decision Framework
Use this fast decision flow to narrow your options:
- Need strict transactional focus and clean separation? Start with Postmark.
- Need flexibility, routing, and deeper domain-level controls? Start with Mailgun.
- Need broad platform adoption and “everything under one roof” options? Start with SendGrid.
After that, validate your shortlist using the step-by-step checklist below.
Step-by-Step Solution
1) Map how your app sends email today
First decide how your application will send email:
- API-only (best for structured errors, metadata, and event correlation)
- SMTP-only (fastest swap for legacy systems)
- Hybrid (API primary, SMTP fallback)
If you are building a new system, API-first is usually easier to operate because you can attach IDs, tags, and correlation data that make debugging faster. The MailCub Documentation is a good reference for the kind of send endpoint and authentication flow your team should validate during evaluation.
2) Require event webhooks (non-negotiable for SaaS)
Before production, confirm the provider supports webhook/event delivery for at least these outcomes:
- processed/accepted
- delivered (or equivalent “delivery confirmed” event)
- deferred
- bounced (hard and soft, if exposed)
- complaint/spam report (if available)
- dropped/blocked (provider-specific)
A safe implementation pattern is:
- Receive webhook
- Validate authenticity
- Enqueue processing
- Update message status in your database
It is also a good practice to store raw payloads for a short retention window to support debugging during incidents.
3) Confirm log visibility and searchability
You need delivery logs that are searchable by:
- recipient
- message ID
- time window
- status
- failure reason
This is what turns “the user didn’t receive the email” from a long investigation into a quick operational check.
4) Understand suppression and bounce behavior
Make sure the provider workflow supports all of the following:
- automatic suppression for hard bounces
- protection against retry storms
- suppression list export/import (important during migration)
- clear distinction between invalid-address failures and temporary failures
This becomes more important as your user base grows and list quality changes over time.
5) Decide whether you need traffic separation
If your product sends both transactional and bulk mail, separation matters. Keep them separate using streams, categories, or subdomains depending on the provider model.
Also keep templates and link behavior consistent per stream. This reduces the risk that bulk traffic creates reputation swings that hurt transactional delivery.
6) Evaluate dedicated IP needs realistically
Dedicated IPs can help, but only in the right conditions.
Dedicated IP may help when:
- you have sustained sending volume
- you can warm up safely
- you have monitoring and staff to manage reputation signals
Dedicated IP can hurt when:
- volume is low or spiky
- warmup is unmanaged
- you treat it as an instant deliverability fix
If your team wants a simpler starting point for transactional email operations, the Transactional Email Service provides a cleaner baseline to build from before adding more complexity.
7) Run a side-by-side test before choosing
Before you finalize the provider, run a controlled side-by-side test for 1–2 days:
- same template
- same recipient domains
- same sending cadence
- webhook capture enabled
Compare outcomes such as:
- deferrals
- bounce reasons
- time-to-delivery patterns
- support ticket volume
This gives you real operational evidence instead of relying on feature marketing alone.
| Provider | Best fit | What engineers like | Watch-outs |
|---|---|---|---|
| Postmark | Transactional-first SaaS | Clean separation model, predictable workflows, strong focus on transactional operations | Ensure the separation model matches your mail types and reporting needs |
| Mailgun | Flexibility + email ops | Domain-level controls, routing patterns, event handling flexibility | Plan tiers/features can vary; validate the exact features you rely on |
| SendGrid | Broad ecosystem stacks | Email API + SMTP options, large adoption footprint, many integrations | Feature breadth can add complexity; verify exactly what you’ll use |
Common Mistakes
- Choosing based on popularity instead of webhooks, logs, and suppression behavior.
- Migrating everything at once with no staged rollout.
- Changing provider, templates, and authentication in the same release.
- Ignoring bounce classification differences between providers.
- Not validating webhook security and silently losing events.
- Buying a dedicated IP without a warmup plan and monitoring process.
Troubleshooting
Webhook events are not arriving
Use this checklist:
- Confirm the endpoint URL is correct.
- Make sure your endpoint returns 2xx quickly.
- Check whether signature/secret validation is failing.
- Handle payload size and timeout limits safely.
- Confirm provider retries are supported and logged on your side.
Bounce rate increases after switching providers
Common causes include authentication misalignment (SPF/DKIM/DMARC) during migration, traffic moved too quickly without warmup, or suppression lists not being migrated.
Fixes usually include slowing the rollout, validating authentication, importing suppression data where possible, and comparing bounce reasons by recipient domain.
Reporting is messy and you can’t segment mail types
Introduce streams, categories, or tags per message type. If needed, split by subdomain and keep transactional templates minimal and consistent.
For your own internal implementation standards, document the exact fields, auth rules, and event tracking requirements in one place using the MailCub Documentation style approach so migrations and audits are easier later.
FAQ
Which is best for transactional email: Postmark, Mailgun, or SendGrid?
It depends on your stack and priorities. Postmark often fits transactional-first workflows, Mailgun fits flexibility and domain-level operations, and SendGrid fits broader ecosystem stacks.
Should I use SMTP or an Email API?
API-first is usually easier to operate because of metadata, structured errors, and event correlation. SMTP is still useful as a fallback or for legacy systems.
What webhook events do I need at minimum?
At minimum: accepted/processed, delivered, deferred, bounced (hard/soft if available), and complaint/spam events. Add dropped/blocked if your provider exposes them.
When does a dedicated IP make sense?
When you have stable volume, a warmup plan, and monitoring capacity. Otherwise, shared pools may be simpler and safer.
How do I migrate without hurting deliverability?
Use a staged rollout, keep templates stable, avoid changing authentication and content at the same time, and compare outcomes using webhooks and logs.
What’s the minimum must-have feature checklist?
Email API or SMTP, event webhooks, searchable logs, suppression management, and a support path that matches your operational risk.
Conclusion
Postmark, Mailgun, and SendGrid can all support production SaaS email. The best fit depends on your sending model, your observability requirements, and how much operational control your team wants.
The safest way to choose is not by feature lists alone. Use a structured evaluation process: decide API vs SMTP, require webhooks, verify log visibility and suppression behavior, then run a side-by-side test. That process reduces surprises far more than brand comparisons.
If you want a clean transactional setup reference while evaluating providers, use the MailCub Documentation for implementation planning and the Transactional Email Service to compare against your current requirements. For scaling and plan considerations, review MailCub Pricing.