fix lower boundaries

Author: joseferben

packages/letters/letters.0.4.0/opam

@@ -11,15 +11,15 @@ bug-reports: "https://github.com/oxidizing/letters/issues"
 depends: [
   "dune" {>= "2.7"}
   "ca-certs" {>= "0.2.1"}
-  "colombe" {>= "0.7.0"}
+  "colombe" {>= "0.11.0"}
   "containers" {>= "3.13.1"}
   "fmt" {>= "0.8.8"}
   "fpath" {>= "0.7.0"}
   "lwt" {>= "5.2.0"}
-  "mrmime" {>= "0.3.1"}
+  "mrmime" {>= "0.6.1"}
   "ocaml" {>= "4.08.1"}
   "ptime" {>= "0.8.5"}
-  "sendmail" {>= "0.7.0"}
+  "sendmail" {>= "0.11.0"}
   "tls-lwt" {>= "1.0.4"}
   "tls" {>= "1.0.4"}
   "x509" {>= "0.9.0"}