Automatically moving marked mails?

[Jorey Bump]

Ian Eiloart wrote, at 07/09/2009 10:46 AM:
> 
> --On 9 July 2009 09:54:31 -0400 Adam Tauno Williams <adam at morrison-ind.com> 
> wrote:
> 
>>>> Ian Eiloart wrote, at 07/09/2009 05:39 AM:
>>>>> Except that the sieve server ought to be on the border MTA, so that the
>>>>> user can tell the server to reject the message at SMTP time.
>>>> That's not feasible for mail with multiple recipients.
>>> It is if your rule is to reject all email from a specific sender.
>> No, because the MTA either accepts or rejects a message [in
>> connection].
> 
> Not true. The MTA can decide *per recipient* whether to accept mail from a 
> specific sender. 

How?

> It's true that the MTA hasn't seen the message content at 
> this point, but it does have enough information to determine - for example 
> - whether the sender is a member of a mailing list, or is on a recipient's 
> blacklist or whitelist. We do a lot of that.

Please elaborate. What kind of feedback does the sender get when you
reject a message during the SMTP transaction for one recipient, but
deliver it for others?