When your website or software needs to send email, you have two main routes: connect to an SMTP relay, or call an email API over HTTPS. Both deliver messages; they differ in how you integrate, how much control you get and how you track results. For Canadian organizations, both also raise the same questions about CASL and where data is processed.
The short answer
- Choose SMTP if your software already has an SMTP settings screen (WordPress, Magento, many accounting and booking systems) and you want to be sending within minutes.
- Choose the API if you are building or maintaining your own application and want structured responses, templates and event webhooks.
Side-by-side comparison
| SMTP relay | Email API | |
|---|---|---|
| Setup | Enter host, port, username and password in your software | Write code that calls HTTPS endpoints with an API key |
| Best for | Existing platforms and plugins | Custom applications and SaaS products |
| Feedback | Delivery reports in the Mailpro interface | Message IDs in responses plus real-time webhooks |
| Templates | Usually built in your own application | Can be stored and called by ID, with language variants |
| Firewall | Needs an outbound SMTP port open | Uses standard HTTPS |
Scenarios from Canadian businesses
A Shopify or WooCommerce retailer in the Prairies
The store already sends order emails through a built-in mailer. Pointing it at an SMTP relay improves deliverability without touching code. See our SMTP server for Canada page.
A fintech or SaaS company in Toronto or Vancouver
The product sends account verifications, security alerts and statements. The API fits better: developers can pick English or French templates per user, log message IDs and react to bounces through webhooks. Our FAQ on the three webhook types explains the events.
An agency managing many client sites
Often a mix: SMTP for client CMS sites, the API for custom builds. Both run through the same Mailpro account and reporting.
Compliance is the same either way
CASL does not care which protocol you use. What matters is the content: transactional messages such as receipts and password resets are largely exempt from the consent requirement, while anything promotional needs consent, identification and an unsubscribe link. Keep marketing and transactional streams separate. On the privacy side, PIPEDA’s accountability principle and Quebec’s Law 25 apply to the personal data in these emails whichever route you choose. Mailpro processes both SMTP and API traffic in Switzerland, outside US jurisdiction, with TLS 1.3 encryption, and is GDPR-native, which helps if you also email customers in Europe (see our GDPR page).
Security considerations
Both methods can be secure if you manage credentials carefully. With SMTP, use port 587 with STARTTLS or port 465 with implicit TLS, and create separate credentials for each application so one compromised plugin doesn’t expose everything. With the API, keep keys on the server side, never in front-end code, and rotate them when staff or contractors change. In both cases, traffic to Mailpro is encrypted with TLS 1.3 and processed in Switzerland.
Handling peak periods
Canadian e-commerce volume clusters around Black Friday, Cyber Monday and Boxing Day, and around Thanksgiving for food and travel businesses. If your application sends one confirmation per order, those days can multiply your usual volume. The API handles bursts well because each request is independent and returns immediately; an SMTP connection can also cope, but check your application’s own queue and retry settings before the season starts. Either way, warm up any new sending domain in the weeks before a peak rather than on the day.
Moving from another provider
Switching an SMTP integration is usually a matter of changing four settings. Switching an API integration takes more work, because endpoints and payloads differ. Many teams move SMTP traffic first, confirm deliverability, then migrate API calls service by service. Update your SPF record to include Mailpro and publish the new DKIM key before you switch, so there is no gap in authentication.
Tracking and troubleshooting
With SMTP, you see delivery and engagement data in the Mailpro dashboard. With the API, you can also pull data programmatically and receive webhook events. Our page on email API statistics explains the metrics, and delivery status for transactional email covers each status code.
Getting started
Whichever you choose, authenticate your sending domain with SPF and DKIM first. Then read the API documentation or configure your SMTP credentials. For marketing emails triggered by behaviour rather than code, consider automated emails instead. More on the product at email API for Canada.