Most American small businesses send far more email from software than from people: contact-form notifications from WordPress, order confirmations from WooCommerce, invoices from accounting tools, alerts from booking systems. Left on default settings, those messages often go out through a shared web-hosting server with no authentication, and increasingly end up in spam. An SMTP relay fixes that by sending them through a dedicated, authenticated service.
Why the default settings no longer work
Since 2024, Gmail and Yahoo have required senders to authenticate their mail, and bulk senders must also publish a DMARC policy and keep spam complaints low. Microsoft has introduced comparable rules for Outlook.com. Emails sent from a generic hosting server that cannot sign for your domain often fail these checks. Many residential and cloud networks in the US also block outbound port 25, the traditional SMTP port, so software that relies on it may not send at all.
What Mailpro’s SMTP relay adds
- Authentication for your domain with SPF, DKIM and DMARC, so mailbox providers can verify that the message really comes from you.
- Secure connections using authenticated SMTP and TLS 1.3 encryption.
- Delivery tracking: see whether each message was delivered, bounced or opened, in SMTP statistics.
- Swiss data hosting: message logs are stored in Switzerland on private infrastructure, outside US jurisdiction.
Typical US setups
WordPress and WooCommerce
Install an SMTP plugin, enter Mailpro’s server details and send a test. Contact forms and order emails then leave through the relay. Our guide to the best SMTP server for WordPress goes through the steps.
Accounting and invoicing
If your invoicing software supports custom SMTP, routing invoices through Mailpro gives you delivery logs you can check when a client says they never received a bill.
CRMs and line-of-business tools
Many CRMs, help desks and practice-management systems used by US professional firms allow a custom SMTP server. Using one relay for all of them keeps authentication consistent across your domain.
Transactional and promotional: know the difference
Under the CAN-SPAM Act, transactional messages such as receipts are largely exempt from opt-out and postal-address requirements, but promotional emails sent through SMTP are not. If you send newsletters through the relay, include an unsubscribe link and your physical address, or use Mailpro’s campaign tools, which add the unsubscribe link for you. See US email marketing law for more.
SMTP or API?
SMTP is the fastest route for existing software. If you are building your own application, compare it with the API in API vs SMTP. New to the protocol? Start with what is SMTP?
Pricing is based on emails sent, and you can test the relay with 500 free credits. In Mailpro’s own customer survey, users rate email deliverability 9.6/10.