diff --git a/packages/letters/letters.0.4.0/opam b/packages/letters/letters.0.4.0/opam
new file mode 100644
index 00000000000..895f397eb7f
--- /dev/null
+++ b/packages/letters/letters.0.4.0/opam
@@ -0,0 +1,53 @@
+# This file is generated by dune, edit dune-project instead
+opam-version: "2.0"
+synopsis: "Client library for sending emails over SMTP"
+description: "Simple to use SMTP client implementation for OCaml"
+maintainer: ["Miko Nieminen <miko.nieminen@iki.fi>"]
+authors: ["Miko Nieminen"]
+license: "MIT"
+homepage: "https://github.com/oxidizing/letters/"
+doc: "https://oxidizing.github.io/letters/"
+bug-reports: "https://github.com/oxidizing/letters/issues"
+depends: [
+  "dune" {>= "2.7"}
+  "ca-certs" {>= "0.2.1"}
+  "colombe" {>= "0.7.0"}
+  "containers" {>= "3.13.1"}
+  "fmt" {>= "0.8.8"}
+  "fpath" {>= "0.7.0"}
+  "lwt" {>= "5.2.0"}
+  "mrmime" {>= "0.3.1"}
+  "ocaml" {>= "4.08.1"}
+  "ptime" {>= "0.8.5"}
+  "sendmail" {>= "0.7.0"}
+  "tls-lwt" {>= "1.0.4"}
+  "tls" {>= "1.0.4"}
+  "x509" {>= "0.9.0"}
+  "alcotest" {>= "1.1.0" & with-test}
+  "alcotest-lwt" {>= "1.1.0" & with-test}
+  "yojson" {>= "1.7.0" & with-test}
+  "odoc" {with-doc}
+  "ocamlformat" {dev}
+]
+build: [
+  ["dune" "subst"] {dev}
+  [
+    "dune"
+    "build"
+    "-p"
+    name
+    "-j"
+    jobs
+    "@install"
+    "@runtest" {with-test}
+    "@doc" {with-doc}
+  ]
+]
+dev-repo: "git+https://github.com/oxidizing/letters.git"
+url {
+  src: "https://github.com/oxidizing/letters/archive/0.4.0.tar.gz"
+  checksum: [
+    "md5=fd4908095f51b81bc37d57b6d08a0df3"
+    "sha512=8b1513c52866dc5f582024cb55ca8139ae7f6c62e3d1500e664a9d11ba0ee3877b66335f2137e8052310e3cc5b9f760fd6110952692c619d7517654e7337b9ed"
+  ]
+}