smtp-server
1 Usage
2 Reference
tls-encode-proc/  c
current-smtp-hostname
envelope
start-smtp-server
smtp-limits?
make-smtp-limits
Bibliography
8.3

smtp-server

Bogdan Popa <bogdan@defn.io>

This module module provides a minimal implementation of RFC 5321 [RFC5321] that can receive e-mail messages.

1 Usage

(define stop
  (start-smtp-server println))

The example above starts an SMTP server on localhost port 25 that prints all incoming e-mail to standard out. Calling the stop function terminates any connections in flight and stops the server.

See "example/" in the source code repository for an example with STARTTLS support.

2 Reference

value

tls-encode-proc/c : 
(-> input-port?
    output-port?
    #:mode 'tcp
    #:encrypt 'tls
    #:close-original? #t
    (values input-port? output-port?))
The contract for TLS-encoding procedures. See also ports->ssl-ports.

Controls the host name displayed to clients.

struct

(struct envelope (sender recipients data)
    #:extra-constructor-name make-envelope)
  sender : bytes?
  recipients : (listof bytes?)
  data : bytes?
Represents the sender, recipients and contents of a receieved e-mail.

procedure

(start-smtp-server handler    
  [#:host host    
  #:port port    
  #:limits lim    
  #:tls-encode tls-encode])  (-> void?)
  handler : (-> envelope? void?)
  host : string? = "127.0.0.1"
  port : (integer-in 0 65535) = 25
  lim : smtp-limits? = (make-smtp-limits)
  tls-encode : (or/c #f tls-encode-proc/c) = #f
Starts an SMTP server that listens on host and port and returns a function that will stop the server when applied.

Successfully-received e-mails are passed to handler. When the handler raises an exception, the server notifies the client that the message has been rejected.

The #:limits arguments can be used to customize various security limits.

If the optional #:tls-encode argument supplies a tls-encode-proc/c value, the server advertises STARTTLS support and clients may opt in to TLS encryption.

procedure

(smtp-limits? v)  boolean?

  v : any/c

procedure

(make-smtp-limits [#:max-connections max-connections 
  #:max-line-length max-line-length 
  #:max-envelope-length max-envelope-length 
  #:session-timeout session-timeout]) 
  smtp-limits?
  max-connections : exact-positive-integer? = 512
  max-line-length : exact-nonnegative-integer? = 1024
  max-envelope-length : exact-nonnegative-integer?
   = (* 10 1024 1024)
  session-timeout : (and/c number? positive?) = 300
Security limits allow you to configure various security-related limits on an SMTP server.

The #:max-connections argument controls the maximum number of concurrent client connections that the server will accept at a time.

The #:max-line-length argument controls the maximum length in bytes of each line received from a client may be. The server will reject lines longer than this amount.

The #:max-envelope-length argument controls the maximum length of incoming e-mails from clients. The total length of an envlope includes the length in bytes of the sender and the recipients list as well as the message data.

The #:session-timeout argument controls the maximum amount of time, in seconds, that a client session may be open for.

Bibliography

[RFC5321] J. Klensin, “Simple Mail Transfer Protocol.” 2008. https://www.ietf.org/rfc/rfc5321.html