Re: MTA or SMTP proxy?

Jozsef Kadlecsik a écrit :
> On Fri, 3 Jul 2009, Gábor Lénárt wrote:
> 
>> On Fri, Jul 03, 2009 at 09:55:40PM +1000, Barney Desmond wrote:
>>>> Recently I am thinking of reimplementing our MX servers. Of course rcpt
>>>> check is a must, also I should not generate NDRs later, I should only accept
>>> <snip>
>>>
>>> This is all very standard behaviour for an MTA. Recipient checking is
>>> a very common task for most Postfix users. Regardless of what you
>>> expect or want, SMTP is a store-and-forward protocol - queues are a
>>> strong component for an MTA.
>> I don't think so, SMTP itself is just a protocol, you can use it without
>> having and storage too. It's another question that how useful it is then ...
> 
> SMTP is a store-and-forward protocol, it does require queues. You cannot 
> simply wave aside this requirement.
> 

This is wrong. an smtp proxy (without a queue) is more than feasible.
some people even use it (assp, ...). smtp does not mandate a queue.

> I think it cannot be solved with an SMTP proxy "without queues" either: 
> the final destination must queue the message first. After that it can 
> attempt a local delivery, which may fail, 

In theory at least, a final delivery MTA could deliver directly, without
a queue. of course, there is the problem of privileges. but for example,
on a system where the whole mailstore belongs to a single (virtual)
uid:gid, then the final MTA can deliver directly to a maildir. some
people even think this should be the way to deliver mail ("immediate
delivery").

> for example due to the user 
> being over quota. Therefore at the proxy side you also have to maintain 
> the mail queue.