Bug 29330: (QA follow-up) Change to message/rfc822

This content-type might be more appropriated to use as a temporary
label for the serialized email message with attachments.

WARNING: perl -cw tells you that the constant is redefined. This has
to do with an already existing module dependency loop of Letters.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

C4/Letters.pm

@@ -40,6 +40,8 @@ use Koha::Patrons;
 use Koha::SMTP::Servers;
 use Koha::Subscriptions;
 
+use constant SERIALIZED_EMAIL_CONTENT_TYPE => 'message/rfc822';
+
 our (@ISA, @EXPORT_OK);
 BEGIN {
     require Exporter;
@@ -1230,7 +1232,7 @@ sub ResendMessage {
   This routine picks the I<content> of I<letter> and generates a MIME
   email, attaching the passed I<attachments> using Koha::Email. The
   content is replaced by the string representation of the MIME object,
-  and the content-type is updated to B<MIME> for later handling.
+  and the content-type is updated for later handling.
 
 =cut
 
@@ -1259,7 +1261,7 @@ sub _add_attachments {
         );
     }
 
-    $letter->{'content-type'} = 'MIME';
+    $letter->{'content-type'} = SERIALIZED_EMAIL_CONTENT_TYPE;
     $letter->{content} = $message->as_string;
 
     return $letter;
@@ -1409,7 +1411,7 @@ sub _send_message_by_email {
             subject  => "" . $message->{subject}
         };
 
-        if ( $message->{'content_type'} && $message->{'content_type'} eq 'MIME' ) {
+        if ( $message->{'content_type'} && $message->{'content_type'} eq SERIALIZED_EMAIL_CONTENT_TYPE ) {
 
             # The message has been previously composed as a valid MIME object
             # and serialized as a string on the DB