Transactional Email: Transactional Email Best Practices: OTPs, Receipts, and Notifications That Always Deliver
How to set up transactional email infrastructure correctly so critical emails never land in spam.
Transactional vs marketing email — keep them separate
Sending OTPs through the same infrastructure as bulk campaigns risks deliverability contamination. One spam complaint on a marketing campaign can delay a customer's one-time password by minutes — or worse, land it in spam.
Transactional emails (OTPs, receipts, password resets, order confirmations) are expected by recipients and have legal delivery requirements. Marketing emails are unsolicited and carry spam risk. Mixing them on the same domain or IP pool puts your critical emails at risk.
Use a dedicated transactional sending domain and IP pool so your most critical emails are never affected by marketing performance. SpaceCRM supports separate infrastructure for transactional and marketing email through its Send API.
Setting up transactional email infrastructure
Start with a dedicated sending domain (e.g., mail.acme.com) separate from your marketing domain. Configure SPF, DKIM, and DMARC records specifically for this domain. Never share authentication records between transactional and marketing domains.
Use a dedicated IP pool for transactional email. Shared IPs mean your transactional deliverability depends on other senders' behavior. Dedicated IPs give you full control over your sending reputation.
SpaceCRM's Send API handles infrastructure setup automatically. Authentication, IP warmup, and reputation monitoring are built in — no need to manage separate infrastructure.
Integrating the SpaceCRM Send API
Authentication via API key, a single POST endpoint, and webhook callbacks for delivery events. Integration takes under 30 minutes in any language. The API supports both REST and SMTP interfaces.
Use the API for OTPs, welcome emails, password resets, order confirmations, and notifications. Every send is logged with full event history — delivery status, open time, click time, and bounce reason.
Set up webhook listeners for real-time delivery events. SpaceCRM sends webhooks for sent, delivered, opened, clicked, bounced, and complained events. Use these webhooks to trigger business logic in your application.
Monitoring critical email delivery
Set up webhook listeners for bounce and complaint events. A 2%+ bounce rate on transactional email needs immediate attention — it means your authentication is misconfigured or your list contains invalid addresses.
Monitor OTP delivery time specifically. Users expect OTPs in under 10 seconds. If p95 delivery exceeds 30 seconds, review your sending infrastructure, check for DNS propagation issues, and verify your API response times.
Track delivery rates by email type separately. OTPs should have 99%+ delivery rates. If they drop below 98%, investigate immediately — a failed OTP means a locked-out user and a support ticket.
Best practices for transactional email content
Keep transactional emails plain and functional. No marketing messages, no upsells, no promotional content mixed into OTPs or receipts. Including marketing in transactional emails violates CAN-SPAM and damages deliverability.
Use clear, specific subject lines: 'Your verification code is 482931' not 'Verify your account.' The subject line should tell the recipient exactly what the email contains without requiring them to open it.
Include a helpful preheader that complements the subject line. For OTPs: 'This code expires in 10 minutes.' For receipts: 'Your order #12345 confirmation.' Preheaders appear in inbox previews and reduce unnecessary opens.