From: /dev/rob0 (rob0gmx.co.uk)
Date: Mon Aug 21 2006 - 17:50:43 CDT

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On Monday 21 August 2006 17:32, Peter wrote:
> I presume that relay_recipient_maps is only used for a small setup
> (like mine) or am I missing something?

Missing something, I think. The bigger you are, the more important it
is that you reject invalid recipients in SMTP before DATA. Smaller
sites can get away with using a catchall address, or even generating
the backscatter, as they are too small to be noticed.

Please do not confuse "get away with" and "do the right thing".
Backscatter is UBE, and it is wrong even on a small scale.

> The production server coming
> along will be a gateway/relay for up to 20 domains -each with
> hundreds of end users.

You must maintain (or query via network) a list of all valid addresses
in each of those domains.

A popular workaround is reject_unverified_recipient, wherein your
verify(8) service consults the final-destination MTA and asks to
validate whilst the connecting client waits.
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