and greylisting

John Sutton
Wed Oct 6 08:58:57 UTC 2004

Hi there

Has anybody else had problems with's servers and 
greylisting?  I've just checked my logs and found that they don't re-send 
after receipt of a 452.  They do at least bounce the message so not 
completely broken!  Their website gives the impression (sic) that they know 
what they are doing, so I thought to canvas wider opinion before I stick my 
neck out any further ;-)


----------  Forwarded Message  ----------
Subject: Re: 452 delivery problems
Date: Tue, 5 Oct 2004 15:49:40 +0100
From: John Sutton <>
To: "Donald ------snipped

Hi Donald

Sorry about the inconvenience!  I did respond to Craig but he never got back
to me.

Re greylisting, please refer

The problem is that emailsystems mail server is not RFC2821 compliant.
Compliance with the SMTP protocol requires that:

1) the 452 code is treated as a *temporary* failure:

   4yz   Transient Negative Completion reply

rather than a permanent failure, which is a 5yz:

   5yz   Permanent Negative Completion reply

2) re-transmission is attempted after a suitable delay which *should* be 30
mins or longer:

   The sender MUST delay retrying a particular destination after one
   attempt has failed.  In general, the retry interval SHOULD be at
   least 30 minutes; however, more sophisticated and variable strategies
   will be beneficial when the SMTP client can determine the reason for

In fact, if the email is re-presented anytime after 4.5 mins, and before 1
week after initial presentation, then it will be accepted by our system.  I
don't know if their system is either failing to retry at all or is retrying
10 times in the next 10 seconds, I've seen both forms of pathological
behaviour before!

Let me know if emailsystems are either unable or unwilling to fix their
systems and I will specifically exclude them from our greylisting.  But I
have to say, for an organisation attempting to run a business delivering
email, they really should implement SMTP.

Best regards
John Sutton

John Sutton
SCL Internet
Tel. +44 (0) 1239 711 888

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