Which Provider Keeps Your Email Out of Spam—and Off Blocklists?
If your emails aren’t landing in the inbox, your SMTP relay service might be the reason. Whether you’re a web host, SaaS company, or transactional sender, choosing the right relay provider is critical for reliable delivery, scalability, and IP reputation.
In this post, we compare the best SMTP relay services of 2025 based on features, pricing, deliverability, spam protection, and ease of integration.
New to this topic? Start with our Email Deliverability Hub
What is an SMTP relay service?
An SMTP relay service routes your outbound emails through a third-party infrastructure that handles delivery, spam filtering, reputation management, and IP warmup.
Instead of maintaining your own mail servers, you plug into a trusted platform that ensures your messages get where they’re supposed to go—fast and safely.
At-a-glance comparison table
| Service | Best For | Deliverability Tools | Outbound Spam Protection | Shared IP Management | Pricing (Starting) |
|---|---|---|---|---|---|
| MailChannels | Hosting Providers & Resellers | Yes (ResponseAnalytics, Auth Checks) | ✅ Industry-Leading | ✅ Dynamic Pool Isolation | Custom Pricing |
| SendGrid (Twilio) | High-Volume Marketing | Yes (Email Activity Feed) | ❌ None | Basic Shared Pool | Free tier; Paid from $19.95/month |
| Mailgun (Sinch) | Developers & SaaS | Yes (Logs & Validation APIs) | ❌ None | Basic Shared Pool | Free tier; Paid from $35/month |
| Postmark | Transactional Email | Yes (Inbox Performance) | ❌ None | Dedicated IPs only | $15/month (10,000 emails) |
| Amazon SES | Technical Users at Scale | Yes (via CloudWatch) | ❌ None | Very limited control | Pay-as-you-go |
| SMTP2GO | Small Businesses | Yes (Reputation Monitoring) | ❌ Minimal | Yes, Basic | Free tier; Paid from $10/month |
Why spam filtering matters for SMTP relay
Most SMTP relay providers focus only on inbox placement—not outbound spam control.
But if you’re a shared hosting provider, you face unique challenges:
- One compromised customer can send spam through your relay.
- Shared IPs can get blocklisted without warning.
- Your brand reputation is at risk—even if you didn’t send the spam.
Only MailChannels includes built-in outbound spam filtering, which quarantines bad traffic before it harms your deliverability.
🔗 Learn more: How MailChannels Detects Outbound Spam and Phishing
Key factors to compare
1. Deliverability Infrastructure
Does the service offer:
- Shared or dedicated IP pools?
- Domain reputation tracking?
- Automatic IP warm-up?
Postmark and MailChannels excel at maintaining deliverability through tight IP control.
2. Spam Detection & abuse prevention
Most providers leave you responsible for abuse handling. This can lead to:
- Blocklisting
- IP reputation damage
- Legal and compliance issues
MailChannels routes, inspects, and filters traffic at the network level—preventing abuse before it hits.
3. Ease of integration
Most SMTP relay services offer:
- API access
- SMTP compatibility
- SDKs or plugins for platforms like WordPress, Laravel, cPanel
Mailgun and SMTP2GO are known for developer-friendly APIs; MailChannels offers seamless cPanel integration for hosts.
4. Support & transparency
Not all support is created equal. Some platforms limit support to ticket systems or charge for SLA access.
MailChannels and Postmark both offer strong documentation and support responsiveness for enterprise users.
Best SMTP relay for your use case
| Use Case | Recommended Provider |
|---|---|
| Shared Hosting or Reseller Hosting | ✅ MailChannels (spam filtering, shared IP defense) |
| Transactional SaaS Email | Postmark or Mailgun |
| Marketing Campaigns at Scale | SendGrid |
| Low-Cost, Low-Volume Sending | SMTP2GO or Amazon SES |
| Security-Conscious Organizations | MailChannels (phishing and abuse control) |
Don’t let the cheapest option cost you more
Saving a few dollars on email relays can result in:
- Lost inbox placement
- Emergency delisting efforts
- Blocked domains or accounts
- Support team overload from email issues
Want peace of mind with every email sent? See why hosting providers rely on MailChannels.
Related reading
- IP Reputation Management: Why It Matters
- What Does “550 Spam Content Detected” Mean?
- How Do Spam Traps Work?
- What Is a Suppression List?