David Sharpe wrote:

> Recently (Mid-January 2008) Hotmail has developed some intermittent 
> delivery problem with email being
> sent through our server.
> 
> * A new message to a hotmail address is discarded by Hotmail and never 
> shown to the user
> * A reply to a message - to a hotmail address - is delivered reliably
> * All email from Hotmail to our server is delivered reliably
> 
> Mail logs show mail is queued correctly on the Hotmail servers in all 
> cases - any suggestions as to why
> mail is suddenly being silently dropped?

Their filters are dumb. You can get most email through by making the 
messages look like replies by adding fake References/In-Reply-To 
headers. Before your normal dnslookup router add a router like this:

dnslookup_hotmail:
   driver              = dnslookup
   condition           = ${if match_domain{${lookup 
dnsdb{>:defer_never,mxh=$domain}{$value}{}}}{*.hotmail.com}{true}{false}}
   transport           = remote_smtp
   headers_remove      = User-Agent
   headers_add         = ${if !def:h_References:{References: 
<[EMAIL PROTECTED]>\n}}\
                         ${if !def:h_In-Reply-To:{In-Reply-To: 
<[EMAIL PROTECTED]>\n}}
   ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
   no_more

The "headers_remove = User-Agent" line is something entirely different 
that tends to help. You'll find many references on the web to hotmail 
blocking certain messages that contain Thunderbird in the User-Agent 
header, but allowing through messages that are exactly the same, but 
without the User-Agent header. I tested this myself a while back and it 
was true.

This information comes with no guarantee. For all I know hotmail may 
turn around one day and start blocking messages with fake References 
headers. They're not at the moment though.

MikeC2

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