what's wrong with my headers?

my messages are filteredin hotmail

[keurkoop]

I'm operating a site similar to Friendster where users invite their friends. For the last weeks these invitations are blocked by Hotmail and put into the junk mail folder.

People tell me I need to change my header but I have no idea what to change. Here's an example of a header for an email message:

Return-Path: <[e-mail]>
Received: from example.com (example.com [69.xx.xx.xx])
by server1.mail-example.com (8.12.7/8.12.6) with ESMTP id i0FKuWTm097304
for <[e-mail]>; Thu, 15 Jan 2004 12:56:32 -0800 (PST)
(envelope-from [e-mail])
Received: (from example@localhost)
by example.com (8.11.6/8.11.6) id i0FKq0905022;
Thu, 15 Jan 2004 21:52:00 +0100
Date: Thu, 15 Jan 2004 21:52:00 +0100
Message-Id: <[e-mail]>
To: [e-mail]
From: [e-mail]
Subject: Uitnodiging
Mime-Version: 1.0
Content-type: text/plain
X-UIDL: STD"!jD`"!G3@"!B\!

[edited by: jatar_k at 9:30 pm (utc) on Jan. 15, 2004]
[edit reason] generalized urls, ips, server names [/edit]

[jatar_k]

Welcome to WebmasterWorld keurkoop,

you could be getting bumped just based on the subject too.

what is "X-UIDL"?

[coopster]

>>what is "X-UIDL"?

Hmmm...

<edit>edited by coopster to remove previous submissions until a satisfactory answer has been discovered<edit> :)

The only *good* answer I've found so far was here...

h**p://mail.gnome.org/archives/balsa-list/2002-June/msg00080.html

...they aren't standard and you cannot make assumptions about their availability, syntax or semantics.

[edited by: coopster at 8:13 pm (utc) on Jan. 16, 2004]

[bcolflesh]

I found one too -

mail.gnome.org/archives/balsa-list/2002-June/msg00081.html

I guess the X- part signifies that the MUA is sending a non-standard (not in the RFCs) header - if you write or alter an MUA you would use the X- to prepend your custom headers.

[bcolflesh]

Ahh - from:

packetstormsecurity.nl/9906-exploits/ms.outlook.DoS.txt

"Synopsis: MUA's use a messages uidl as part of a pop transaction to check whether they have received the message before (most include other checks also). Usually the field is calculated when the message is first read by the popper. A lot of poppers will store the uidl for that message in an X-UIDL: header to avoid having to recalculate it every time the client checks thier e-mail. However, mail messages may arrive into a mailbox with a predefined X-UIDL: header. Most popper daemons will use this header instead of calculating a new header."

[Dreamquick]

Basically anything that begins with an "X-" isn't part of the protocol and is very much an application specific freetext variable.

The first relevant item I found mentioning of X-UIDL with relation to spam was a post on Exim.org's mailing lists archive from 2001;

Incoming messages should not have a X-UIDL header. They are supposed to
only be used by a pop daemon so a client can avoid downloading messages it
has already copied, ie when "leave messages on server" is checked. Spammers
add an X-UIDL header to their message to try and mess with that scheme,
possibly hoping you will get multiple copies of their message (increaing the
chances you will read it)

I don't know if that's the problem here as I suspect the header may have been added as the message was downloaded. I think it's more likely the problem is that something about the message content is being flagged as spammy.

I'd be tempted to put the message (as delivered complete with headers) through the spamcop engine to watch for any weird stuff and then through a spam-assasin filter to see what score it would get.

- Tony