Milter-greylist

Michael Menge a \ufffdcrit :
> Also i don't think longer delay will reduce any spam. If it is a regular 
> mailserver it will only delay legetim mail. If it is a spammer who 
> retries it will have success after the longer delay, if not the short 
> delay would do the work also, (or have you seen any spammers that retry 
> after 4 minutes but not after 14?)

Greylisting works ONLY for non-regular MTAs, I think we agree here. 
That's why it is best to target it on clients who are supposed to be 
non-regular MTAs (ie spambots), for example by means of RBLs.

Currently the vast majority of spambots do not intentionally retry, 
except a recently-growing percentage of them who retry 2 or 3 times in 
intervals of 10 minutes (so YES, there are spammers who retry after 10 
minutes but not after 30 minutes, to illustrate your 4/14min. example). 
So setting a longer delay (1 hour) for suspicious clients *do* help 
blocking spam by catching these 3-time-retry spambots. Real MTAs will 
retry up to five days, so they should pass through long greylisting, in 
the event one of them were accidentally listed as "suspicious".

> 
> Ther are may MX-Server out ther that don't use SRS and with 40.000 
> accounts there are always users that use an MX-server that don't use SRS 
> and which
> is not on a whitelist. The only way would be to allow the user to 
> whitelist his forwarding mailserver, but as i don't have any way for a 
> normal user to figure out which is the forwarding mailserver i can't use 
> SPF to reject emails.

DNS whitelists greatly help for this. And I don't consider unfeasible to 
inform my users that SMTP servers which don't conform to "best 
practices" are exposed to longer delivery delays than well-configured ones.

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