Re: [courier-users] courier-mta and amavis-new +clamAV

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On Wed, 31 Oct 2007, João Vale wrote:

>> >> It falls over flat on it's
>> >> face the moment it is exposed to multi-homed senders
>> > [...]
>> >> There are perfectly valid reasons why one might want to
>> > > run their systems with such a setup (network failure redundancy
>> > > or peering arrangements).
>> >
>> > Oh... Sure ! Though, I would say that such an (static, complicated)
>> > architecture should be quite rare for spammers (very easy to
>> > blacklist).
>> > So in *most* cases greylisting is perfectly adapted.
>>
>> The point is that all such non-spamming setups (e.g. gmail) would need
>> to be whitelisted for greylisting to work. Otherwise, greylisting will
>> massively delay (possibly to the point of bouncing) mail from
>> multi-homed systems.

> As far as I know, SPF takes care of this. In my setup, Google, for
> example, bypasses greylisting because it has a valid SPF record.

SPF is not mandatory as per the RFC. There are a number of MSPs that are
multi-homed but don't have SPF records. Unless SPF records become
mandatory for SMTP mail, the feature cannot be relied upon.

More to the point, there are many situations where one might send valid
email that would look invalid according to the SPF. It is at best a
half-measure that will yield as many false-postives as it does true
negatives.

In other words, it's an unreliable bodge that just happens to make another
unreliable bodge work in one particular case.

Gordan
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