[CentOS] sendmail Deferred mail - reason unknown

[Scott Silva]

on 12-15-2008 12:01 PM Bob Hoffman spake the following:
>  
> 
> ====================================	
> 	The mail logs show that these emails are typically delayed for up to
> 24 hours, sometimes longer.  It appears that several attempts to deliver the
> email are made, with each unsuccessful one showing "Deferred" status in the
> maillog.  After several hours of failed attempts the mail finally goes
> through successfully.  Here is a typical entry (customer name redacted):
> 	
> 	exmx1 : Dec 14 05:28:39 exmx1 sendmail[31574]: mBDIYhEa031574:
> to=<customer at example.com>, delay=00:00:00, xde
> 	lay=00:00:00, mailer=esmtp, pri=41874, relay=mail.example.com.,
> dsn=4.0.0, stat=Deferred
> 	
> 	Unfortunately there is no reason given for the "Deferred" status
> such as "Server unavailable", etc.  
> ====================================
> I would imagine this is a hotmail or yahoo account or something along those
> lines.
Not necessarily

> Deferred does not usually mean bounced or turned into spam, it is more of a
> way of making the user wait for their mail. Yahoo can hold mail for a long
> time, minutes to hours, before they deliver.
Any MTA can defer mail. It doesn't need to be a big bulk provider.
> 
> If you keep resending the deferred mail, you may end up getting auto junked
> though.
> In my minds eye, they are just trying to get people to upgrade as then as if
> by magic, mail to them does not get deferred.
Like I said, not necessarily...

> 
> But in my experience, all deferred mail is usually sent, as far as I know.
> Just 'deferred' for a bit.	
Servers defer mail for many reasons. The message could exceed a size limit
that makes it wait until a certain time.

The server could be over a set load average. It will need to flush its queue
and wait until the load comes down.

It could be greylisting, but I have never seen greylisting set this high.

It could be under a DDOS attack, which makes the server stop listening for a
while.

A log entry with deferred with no other message is probably connection
related. Maybe the mail server is on a small pipe with most of the bandwitth
being used for other reasons at that moment.

There are more reasons than a conspiracy to get you to pay a subscription...


 	


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