{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "https://smtp.standard/schemas/session",
  "title": "SMTP Session",
  "description": "Schema representing an SMTP protocol session as defined in RFC 5321",
  "type": "object",
  "properties": {
    "host": {
      "type": "string",
      "description": "SMTP server hostname or IP address"
    },
    "port": {
      "type": "integer",
      "description": "TCP port number",
      "examples": [25, 465, 587],
      "default": 25
    },
    "secure": {
      "type": "string",
      "enum": ["none", "tls", "starttls"],
      "description": "TLS/SSL security mode. Port 465 uses TLS, port 587 uses STARTTLS"
    },
    "authentication": {
      "$ref": "#/definitions/Authentication"
    },
    "clientHostname": {
      "type": "string",
      "description": "The client's FQDN sent in EHLO/HELO command"
    },
    "extensions": {
      "type": "array",
      "description": "ESMTP extensions supported by the server (from EHLO response)",
      "items": {
        "type": "string"
      },
      "examples": [["STARTTLS", "AUTH LOGIN PLAIN", "8BITMIME", "PIPELINING", "SIZE 52428800"]]
    },
    "transaction": {
      "$ref": "#/definitions/Transaction"
    }
  },
  "definitions": {
    "Authentication": {
      "type": "object",
      "properties": {
        "mechanism": {
          "type": "string",
          "enum": ["PLAIN", "LOGIN", "CRAM-MD5", "DIGEST-MD5", "XOAUTH2"],
          "description": "SASL authentication mechanism"
        },
        "username": {
          "type": "string",
          "description": "Authentication username"
        }
      }
    },
    "Transaction": {
      "type": "object",
      "description": "A single SMTP mail transaction (MAIL FROM through DATA)",
      "properties": {
        "from": {
          "type": "string",
          "format": "email",
          "description": "Envelope sender (MAIL FROM command)"
        },
        "recipients": {
          "type": "array",
          "description": "Envelope recipients (RCPT TO commands)",
          "items": {
            "type": "string",
            "format": "email"
          },
          "minItems": 1
        },
        "messageSize": {
          "type": "integer",
          "description": "Estimated message size in bytes"
        }
      }
    },
    "SMTPCommand": {
      "type": "object",
      "properties": {
        "command": {
          "type": "string",
          "enum": ["EHLO", "HELO", "MAIL", "RCPT", "DATA", "RSET", "VRFY", "EXPN", "NOOP", "QUIT", "STARTTLS", "AUTH"],
          "description": "SMTP command verb"
        },
        "parameters": {
          "type": "string",
          "description": "Command parameters (e.g., FROM:<user@example.com>)"
        }
      }
    },
    "SMTPResponse": {
      "type": "object",
      "properties": {
        "code": {
          "type": "integer",
          "description": "Three-digit SMTP response code",
          "minimum": 100,
          "maximum": 599
        },
        "message": {
          "type": "string",
          "description": "Human-readable response message"
        },
        "enhanced": {
          "type": "string",
          "pattern": "^[245]\\.[0-9]+\\.[0-9]+$",
          "description": "Enhanced status code (RFC 3463) e.g., 2.0.0, 5.1.1"
        }
      }
    }
  }
}