If you’re building SaaS that supports bring-your-own email (or running a business that needs to send transactional email reliably), four providers cover ~95% of the market:
- SendGrid (Twilio) — incumbent, broad feature set
- Postmark — premium transactional, great deliverability
- Resend — newer, developer-first
- AWS SES — cheapest at scale, low-level
- Mailgun — mid-market alternative
Here’s how they compare for transactional email specifically (booking confirmations, password resets, appointment reminders).
At a glance
| Provider | Free tier | Cheapest paid | Cheapest per 1k emails | Deliverability | Setup ease |
|---|---|---|---|---|---|
| SendGrid | 100/day | $19.95/mo (50k) | $0.40 | Good | Medium |
| Postmark | 100 (one-time) | $15/mo (10k) | $1.50 | Excellent | Easy |
| Resend | 100/day | $20/mo (50k) | $0.40 | Very good | Very easy |
| AWS SES | 62k/mo (from EC2) | Pay-per-email | $0.10 | Good | Hard |
| Mailgun | 5k for 3 months | $35/mo (50k) | $0.70 | Good | Medium |
SendGrid
Pros:
- Established (founded 2009, acquired by Twilio 2019)
- Big feature set (templates, marketing emails, A/B testing, dynamic content)
- Strong deliverability with proper setup
- Most platforms support it natively
Cons:
- UI feels dated
- Documentation can be confusing
- Twilio integration occasionally bumpy
- Pricing climbs at higher volumes
Best for: Established businesses with diverse email needs (transactional + marketing + bulk).
Postmark
Pros:
- Best transactional deliverability on the market
- Excellent UX (event tracking, message-by-message visibility)
- Separate streams for transactional vs broadcast
- Simple, transparent pricing
Cons:
- More expensive than alternatives
- Smaller feature set (no marketing emails)
- 100k email cap on plans (above that requires contact)
Best for: SaaS where transactional email deliverability is critical — appointment reminders, password resets, magic links.
Resend
Pros:
- Modern, developer-friendly UX
- Markdown / React-based templates
- API-first design
- Great documentation
- Generous free tier
Cons:
- Newer (founded 2023) — less track record
- Feature set is smaller than incumbents
- No marketing-email features (yet)
Best for: Modern SaaS, developer-led teams, anyone who values UX over breadth.
AWS SES
Pros:
- Cheapest at scale by far ($0.10 per 1k emails)
- Fully integrated with AWS infrastructure
- Massive sending capacity
- Pay-per-email — no monthly minimum
Cons:
- Steep learning curve (sandbox mode, request limits, bounce handling)
- No built-in templates (must use SES + your code)
- Deliverability depends entirely on you setting up domains, DKIM, complaint loops correctly
- UI is barebones
Best for: High-volume sending with engineering resources to manage it. Not for “I just want to send appointment reminders”.
Mailgun
Pros:
- Solid mid-market option
- Strong deliverability for B2B
- Decent feature set
- API-first
Cons:
- Pricing structure is confusing (pay-as-you-go vs flex)
- UX is dated
- Has had reliability incidents in past
Best for: Teams already using Mailgun with no specific reason to switch.
What deliverability really depends on
The provider matters less than:
- Domain authentication — SPF, DKIM, DMARC correctly configured
- Sender reputation — built over the first 1k-10k emails
- Content quality — not spammy, not all-image, personalised
- List hygiene — removing bounced addresses, honouring unsubscribes
- Sending pattern — gradual ramp, not bursty
A well-configured Postmark account and a well-configured SendGrid account both deliver at ~95%+. A misconfigured account on either platform delivers at ~50%.
Pricing comparison: 50k emails/month
For a service business sending 50k transactional emails/month (booking confirms + reminders):
| Provider | Monthly cost | Notes |
|---|---|---|
| AWS SES | ~$5 | Cheapest by far |
| Resend | $20 | 50k included on Pro |
| SendGrid Essentials | $19.95 | 50k included |
| Postmark | $115 | $1.50 per 1k × 50 + setup |
| Mailgun Foundation | $35 | 50k included |
For most service businesses, 50k emails/month is way more than they’ll send. Realistic volume is 5k-15k for most.
For 5k-15k emails/month:
| Provider | Monthly cost |
|---|---|
| AWS SES | ~$1 |
| Resend Free | $0 (under 100/day = ~3k/mo) |
| Resend Pro | $20 |
| SendGrid Free | $0 (100/day = ~3k/mo) |
| Postmark | $15 (10k included) |
For solo / small businesses, AWS SES or Resend Free are functionally free.
What to pick for BYO email in booking SaaS
If you’re an operator using a BYO-email-supporting booking platform like Zedule:
- Solo / small business sending under 3k/month: Resend free tier or SES (~$1/mo)
- Growing business 3k-50k/month: Resend Pro ($20) or Postmark ($15-115)
- Large business 50k+/month: SES if you have engineering, otherwise SendGrid or Resend
Most service businesses fit comfortably in the first two tiers.
Setup complexity
To get a custom-domain email working:
Easy (15-30 min):
- Resend
- Postmark
Medium (30-60 min):
- SendGrid
- Mailgun
Hard (1-3 hours, sometimes a day):
- AWS SES (especially getting out of sandbox mode)
For BYO email in booking software, ease matters because operators (not engineers) are doing the setup. Resend and Postmark are easiest.
Multiple providers?
Some businesses route different email types to different providers:
- Transactional reminders: Postmark (deliverability matters)
- Marketing emails: SendGrid (more features)
- Bulk newsletters: Mailgun
This is overkill for most. Pick one provider and stick with it.