package uspf

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SPF implementation in OCaml


Dune Dependency






uspf is an implementation of the SPF verifier in OCaml compatible with MirageOS.

Published: 13 Mar 2023


µSPF, a SPF verifier/signer in OCaml

uspf is a simple library to check or sign an incoming emails from -data. See RFC 7208.


How to install it?

You must have an OPAM environment. Then, uspf can be installed with:

$ opam install uspf

How to use it?

uspf is a little tool which can be used to verify DNS records from some informations (like where comes from the incoming email - especially, what is the IP address of the sender).

From these informations and the DNS record, we are able to check if the IP address is allowed to send an email under a certain domain-name.

By this way, uspf requires:

  • few informations (the IP address of the sender, its domain-name, etc.)

  • a DNS stack to get records

(* Informations required by uSPF *)
let ctx =
  |> Uspf.with_sender (`MAILFROM address)
  |> Uspf.with_ip ipaddr

(* DNS record *)
let record = Uspf.get ctx sched dns (module DNS)

(* Verification *)
let result = Uspf.check ctx sched dns (module DNS)

From the result, the user is able to emit a new RFC822 field via mrmime:

let field_name, value = Uspf.to_field ~ctx ?receiver result
let () =
  Format.printf "%s: %s\n%!"
    (Mrmime.Field_name.to_string field_name)
    (Unstrctrd.to_utf_8_string value)

uspf has received funding from the Next Generation Internet Initiative (NGI) within the framework of the DAPSI Project.

Dependencies (13)

  1. fmt >= "0.8.9"
  2. dns-client >= "6.1.0"
  3. lwt
  4. dns >= "5.0.1"
  5. domain-name
  6. angstrom >= "0.15.0"
  7. hmap
  8. ipaddr >= "5.2.0"
  9. mrmime >= "0.5.0"
  10. colombe >= "0.4.2"
  11. logs
  12. dune >= "2.8.0"
  13. ocaml >= "4.07.0"

Dev Dependencies (2)

  1. rresult >= "0.7.0" & with-test
  2. alcotest with-test