Re: [apps-discuss] draft-santos-smtpgrey-02: SMTP Service Extension for Greylisting Operations

[Hector Santos <[e-mail]>]

On 2/3/2014 1:57 AM, Ned Freed wrote:
>> On Sat, Feb 1, 2014 at 10:39 AM, Hector Santos <[e-mail]> wrote:
>
>>> For our own implementation and deployments of WCSMTP.
>>>
>>> No collections from other packages was made from a client standpoint.
>>>
>
>> Does anyone else have current or planned implementations of this draft
>> they'd like to discuss?
>
> We see greylisting as something best done by a milter, so we're unlikely to
> implement direct support in our MTA. That said, a milter has the ability to set
> the SMTP response string to anything it wants. The only problem a milter would
> have is changing the EHLO response to include the GREYLISTING extension. AFAIK
> that is not a milter capability. We have a way to do that outside of milter but
> I don't know if other milter-supporting MTAs do.

The service extension keyword was made optional

http://tools.ietf.org/html/draft-santos-smtpgrey-02#section-3.1.1

The intent was to offer a method to expose a retry=time-delay (the 
blocking time) via the keyword and not depend on servers adding and 
clients parsing of 45x response text.


>>> Many Greylisting servers do issue a time hint in their 45x greylisting
>>> responses in various forms.   We can only speculate if other clients are
>>> parsing this non-standard information and leveraging it for their outbound
>>> mail retry scheduling logic.  Our client parses for the common format seen
>>> out there, including the proposed format.
>>>
>
>> Can you point to some of the server implementations that do this?  Are they
>> following the syntax in this draft?
>
> milter-greylist has the ability to return SMTP responses containing the retry
> time. The format is settable, so it should be able to generate something that
> conforms to this RFC.
>
> There are various other milters that support greylisting; I don't know about
> their capabilites.

Yes, for servers, getting the response in is the easy part. The 
benefit is for the client to leverage it for their existing 
rescheduling logic.  Those that do should see a benefit in minimizing 
retries and delivery delays.


-- 
HLS