smtpd

type Envelope struct {
	Sender     string
	Recipients []string
	Data       []byte
}

type Error struct {
	Code    StatusCode // The integer error (status) code
	Message string     // The error message
}

type Peer struct {
	// Server name used in HELO/EHLO command
	HeloName string
	// Username from authentication, if authenticated
	Username string
	// Password from authentication, if authenticated
	Password string
	// Protocol used, SMTP or ESMTP
	Protocol Protocol
	// A copy of Server.Hostname
	ServerName string
	// Network address
	Addr net.Addr
	// TLS Connection details, if on TLS
	TLS *tls.ConnectionState
}

type Protocol string

type Server struct {
	// Server hostname. (default: "localhost.localdomain")
	Hostname string
	// Initial server banner. (default: "<hostname> ESMTP ready.")
	WelcomeMessage string

	// Socket timeout for read operations. (default: 60s)
	ReadTimeout time.Duration
	// Socket timeout for write operations. (default: 60s)
	WriteTimeout time.Duration
	// Socket timeout for DATA command (default: 5m)
	DataTimeout time.Duration

	// Max concurrent connections, use -1 to disable. (default: 100)
	MaxConnections int
	// Max message size in bytes. (default: 10240000)
	MaxMessageSize int64
	// Max RCPT TO calls for each envelope. (default: 100)
	MaxRecipients int

	// New e-mails are handed off to this function.
	// Can be left empty for a NOOP server.
	// If an error is returned, it will be reported in the SMTP session.
	Handler func(peer Peer, env Envelope) error

	// Enable various checks during the SMTP session.
	// Can be left empty for no restrictions.
	// If an error is returned, it will be reported in the SMTP session.
	// Use the Error struct for access to error codes.
	ConnectionChecker func(peer Peer) error              // Called upon new connection.
	HeloChecker       func(peer Peer, name string) error // Called after HELO/EHLO.
	SenderChecker     func(peer Peer, addr string) error // Called after MAIL FROM.
	RecipientChecker  func(peer Peer, addr string) error // Called after each RCPT TO.

	// Enable PLAIN/LOGIN authentication, only available after STARTTLS.
	// Can be left empty for no authentication support.
	Authenticator func(peer Peer, username, password string) error

	// BlackHole is an optimization that allows quietly sending all the
	// incoming message to the big /dev/null in the sky while still
	// maintaining a polite conversation with the client. This behaviour is
	// triggered when the function is set and returns true. In that case the
	// Handler function is not invoked at all. Please note that the
	// Envelope at this stage has its Data field empty.
	BlackHole func(peer Peer, env Envelope) bool

	EnableXCLIENT bool // Enable XCLIENT support (default: false)

	TLSConfig *tls.Config // Enable STARTTLS support.
	ForceTLS  bool        // Force STARTTLS usage.
}

type StatusCode int