Reference
Email dictionary
Reference tables for SMTP reply codes, enhanced status codes, email headers, DNS records and bounce categories, and how Emailit handles each one.
Updated Oct 1, 2026
The email dictionary explains the codes, headers and records you run into when you send email. Use it when you’re reading a bounce message, debugging an SMTP integration or publishing DNS records. Every page also says what Emailit does with each item, so you know whether to act.
Reference pages
Three-digit server replies from 220 to 556, which ones Emailit retries, and the replies Emailit’s own SMTP relay sends.
RFC 3463 codes such as 5.1.1 and 5.7.26, what they mean and how to fix them.
From, Reply-To, Message-ID, DKIM-Signature, List-Unsubscribe and more, and which ones Emailit adds, rewrites or removes.
MX, SPF, DKIM, DMARC, CNAME, PTR, BIMI, MTA-STS and TLS-RPT syntax with examples.
Hard and soft bounces by cause, typical codes, how Emailit classifies them and what to do next.
Short definitions of Emailit concepts and general email terms, from alignment to webhook secret.
Where you see these values in Emailit
- Email detail. Open an email in Email APIEmails and check the Deliveries tab. Each delivery attempt shows the receiving server’s full reply, including the reply code and enhanced status code.
- Webhooks. The
email.attemptedevent includessmtp_code,smtp_enhanced_codeandsmtp_responsefor the failed attempt. See Webhook event types. - Request logs. Replies from Emailit’s own SMTP relay, such as
535 Authentication failed, appear in Email APILogs. See Request logs. - Domain setup. The exact DNS records Emailit asks you to publish are on the domain’s DNS Setup tab. See DNS records.