Add To headers in OmpSs-2 robot email

Cc: Antoni Navarro <antoni.navarro@bsc.es>
Reviewed-by: Aleix Boné <abonerib@bsc.es>

m/hut/ompss2-timer.nix

@@ -29,6 +29,7 @@
     closing = pkgs.writeText "closing.txt"
     ''
       Subject: OmpSs-2 release enters closing period
+      To: star@bsc.es
 
       Hi,
 
@@ -42,6 +43,7 @@
     freeze = pkgs.writeText "freeze.txt"
     ''
       Subject: OmpSs-2 release enters freeze period
+      To: star@bsc.es
 
       Hi,
 
@@ -55,6 +57,7 @@
     release = pkgs.writeText "release.txt"
     ''
       Subject: OmpSs-2 release now
+      To: star@bsc.es
 
       Hi,
 
@@ -69,7 +72,7 @@
         script = ''
           set -eu
           set -o pipefail
-          cat ${mail} | ${config.security.wrapperDir}/sendmail star@bsc.es
+          cat ${mail} | ${config.security.wrapperDir}/sendmail -t star@bsc.es
         '';
         serviceConfig = {
           Type = "oneshot";