Every business that sends emails from its own software eventually faces this choice: connect through SMTP, the protocol email has used for decades, or through an HTTP API designed for developers. Both are available with Mailpro, both deliver through the same infrastructure, and both keep your data in Switzerland. The difference is in how your systems talk to us.
The short version
| SMTP relay | Email API | |
|---|---|---|
| Setup | Enter server, port, username and password in your software | Write code that calls Mailpro’s API |
| Best for | Existing platforms: WordPress, e-commerce plugins, CRMs, accounting tools, printers and scanners | Custom apps, SaaS products, high-volume or event-driven sending |
| Developer effort | Low | Moderate |
| Control and data | Standard email headers | Structured requests and responses, easier templating and metadata |
| Event tracking | Reports in your Mailpro account | Reports plus webhooks pushed to your system |
When SMTP is the better fit
Many tools US small businesses rely on, such as WordPress contact forms, WooCommerce stores, QuickBooks invoices or office multifunction printers, already know how to send through SMTP. You just replace the default settings with the SMTP server details shown in your Mailpro account. No code is needed, and your emails gain authentication and reporting straight away. Read what is SMTP? for background.
When the API is the better fit
If your development team builds its own product, the email API is usually the cleaner option. Your code sends each message with a request and receives a structured response it can log or act on. Webhooks then notify your system about deliveries, bounces and clicks, which makes automated handling of failures straightforward. The developer documentation has the details.
Three US scenarios
A local insurance agency
Quotes and policy documents are sent from an agency management system that supports SMTP. SMTP relay is quick to configure and adds delivery tracking without any development work.
A direct-to-consumer brand on a hosted store
Order emails come from the store platform, while the marketing team sends campaigns from Mailpro. If the platform allows a custom SMTP server, use it; otherwise keep the store’s notifications and focus Mailpro on campaigns and automations.
A SaaS start-up
Sign-up verification, password resets and usage alerts are generated by the application. The API integrates directly with the codebase, and webhooks feed bounce data back to the user database.
Security and reliability compared
Both routes use encrypted connections and authenticated access, so neither is inherently less secure. The practical differences lie in how credentials are handled. SMTP credentials are often stored in plugin settings or device menus, where several people may see them; use a dedicated set of credentials for each application so you can change one without breaking the others. API keys live in your codebase or secrets manager and should never be committed to a public repository. On reliability, SMTP clients usually retry automatically if a connection drops, while an API integration needs its own retry logic for temporary errors, which is simple to add and gives you finer control.
Switching from another provider
Many US businesses move to Mailpro from a provider they outgrew or from a web host’s built-in mail server. For SMTP, the change is usually a matter of updating the host name, port and credentials, then adding Mailpro to your SPF record and publishing the DKIM key. For the API, map your existing calls to Mailpro’s endpoints and run both providers in parallel for a few days before switching all traffic. Avoid switching in the weeks before Black Friday, when any hiccup is most expensive.
What does not change
Whichever route you choose, the rules for US recipients are the same. Transactional messages are largely exempt from CAN-SPAM’s opt-out requirements, but promotional emails are not, wherever they come from. Gmail and Yahoo judge your domain as a whole, so authenticate it with SPF, DKIM and DMARC. Connections are encrypted with TLS 1.3, and data is stored in Switzerland, outside US jurisdiction.
For a wider comparison, read our article on SMTP relay vs email API, and once you are live, track results with API statistics.