The site sends 800 order confirmations daily. From OVH shared SMTP, 12% land in Gmail spam — no logs, no bounce webhook. Host SMTP vs transactional service: the first transports; the second industrializes deliverability, reputation, and traceability.
Host SMTP: smtp.host.com, tight quotas, IP shared with neighbor spammers. Transactional service (Brevo/Sendinblue, Mailgun, Postmark, Amazon SES): API + dedicated SMTP, bounce dashboards, warmed or dedicated IP pool.
Application email comparison
| Criterion | Host SMTP | Transactional service |
|---|---|---|
| Volume / day | Low (hundreds) | Thousands+ |
| Deliverability | Variable | Optimized (reputation) |
| Logs / webhooks | Missing or basic | Optional opens, bounces, events |
| Quotas | Strict | Scalable plans |
| DNS config | Simple SPF | SPF + DKIM + domain auth |
| Cost | Included | Free tier then € |
Sending marketing newsletter from shared SMTP risks order mail on the same reputation.
Host SMTP: OK use cases
Contact form → one internal address.
Very low notification volume.
Dev/staging (never critical prod without test).
Configure at minimum SPF + DKIM if host offers it.
Transactional service: when mandatory
E-commerce, SaaS, bank alerts. Managed bounces, auto suppression lists.
Volume > 500 application emails/day.
Need send proof (compliance, support "I did not receive").
Multi-region with API latency needs.
Typical setup:
- Subdomain
notifications.yoursite.com - Provider DKIM CNAME
- SPF
include:provider - Progressive DMARC
p=quarantinethenreject - Provider API from app (not plain SMTP credentials)
Visible EU actors: Brevo (FR), Mailjet (FR), Scaleway Transactional Email — compare DPA.
Common mistakes
- Gmail SMTP in heavy prod — account suspension
- Same domain marketing + app without separation
- Ignoring hard bounces — dead email base
- Templates without unsubscribe where required (marketing)
The peak: application email is infrastructure
Decide and move forward without blind spots
- Measure outbound volume + spam report rate.
- If e-commerce/SaaS or >500/day → transactional service + subdomain.
- Keep host SMTP for separate human IMAP mail.
- Monitor DMARC reports quarterly.
Google/Microsoft mail for human mailboxes. Compare tool.
Frequently asked questions
Is included SMTP enough for WordPress?
Internal forms yes. Password reset / WooCommerce → transactional recommended.
Marketing vs transactional?
Separate domains/services — shared reputation dangerous.
EU service for GDPR?
Yes DPA + minimization — Brevo, Mailjet, etc.
SPF without breaking mail?
Careful combined includes, DMARC p=none test.
How many "email not received" tickets per month? If >2 with real app volume, shared SMTP is no longer free — it costs support time.