diff --git a/NEWS b/NEWS
index 7f500f1cf..9a2ffc2d2 100644
--- a/NEWS
+++ b/NEWS
@@ -43,6 +43,7 @@ Bug fixes
  - encode HTML entities in JSON data returned by Calendar module (#2598)
  - fixed handling of ACLs on shared calendars with multiple groups (#1854)
  - fixed HTML formatting of appointment notifications for Outlook (#2233)
+ - replace slashes by dashes in filenames of attachments to avoid a 404 return code (#2537)
 
 2.1.1b (2013-12-04)
 -------------------
diff --git a/SoObjects/Mailer/SOGoMailObject.m b/SoObjects/Mailer/SOGoMailObject.m
index aa808d196..85eacf5b9 100644
--- a/SoObjects/Mailer/SOGoMailObject.m
+++ b/SoObjects/Mailer/SOGoMailObject.m
@@ -761,7 +761,7 @@ static BOOL debugSoParts       = NO;
 		        withPath: (NSString *) path
                        andPrefix: (NSString *) prefix
 {
-  NSString *filename, *mimeType;
+  NSString *filename, *mimeType, *filenameURL;
   NSDictionary *currentFile;
 
   filename = [part filename];
@@ -783,14 +783,18 @@ static BOOL debugSoParts       = NO;
 
   if (filename)
     {
+      // We replace any slash by a dash since Apache won't allow encoded slashes by default.
+      // See http://httpd.apache.org/docs/2.2/mod/core.html#allowencodedslashes
+      // See [UIxMailPartViewer _filenameForAttachment:]
+      filenameURL = [[filename stringByReplacingString: @"/" withString: @"-"] stringByEscapingURL];
       currentFile = [NSDictionary dictionaryWithObjectsAndKeys:
                                   filename, @"filename",
                                   [mimeType lowercaseString], @"mimetype",
                                   path, @"path",
                                   [part objectForKey: @"encoding"], @"encoding",
                                   [part objectForKey:@ "size"], @"size",
-                                  [NSString stringWithFormat: @"%@/%@", prefix, [filename stringByEscapingURL]], @"url",
-                                  [NSString stringWithFormat: @"%@/asAttachment/%@", prefix, [filename stringByEscapingURL]], @"urlAsAttachment",
+                                  [NSString stringWithFormat: @"%@/%@", prefix, filenameURL], @"url",
+                                  [NSString stringWithFormat: @"%@/asAttachment/%@", prefix, filenameURL], @"urlAsAttachment",
                                   nil];
       [keys addObject: currentFile];
     }
diff --git a/UI/MailPartViewers/UIxMailPartViewer.m b/UI/MailPartViewers/UIxMailPartViewer.m
index 21aeec623..c973acbb6 100644
--- a/UI/MailPartViewers/UIxMailPartViewer.m
+++ b/UI/MailPartViewers/UIxMailPartViewer.m
@@ -267,7 +267,11 @@
   NSString *extension;
 
   filename = [NSMutableString stringWithString: [self filename]];
-  if (![filename length])
+  if ([filename length])
+    // We replace any slash by a dash since Apache won't allow encoded slashes by default.
+    // See http://httpd.apache.org/docs/2.2/mod/core.html#allowencodedslashes
+    filename = [filename stringByReplacingString: @"/" withString: @"-"];
+  else
     [filename appendFormat: @"%@-%@",
 	      [self labelForKey: @"Untitled"],
 	      [bodyPart nameInContainer]];