[Mimedefang] a case for supporting EXPN/VRFY on an internal s erver

[Brian Leyton]

Gary Funck wrote:
> 
> One of the difficulties we run into with MdF in general and 
> greylisting in particular is that recipient address 
> verification (via the access
> database) is delayed via delay_checks.  So, basically we 
> tempfail messages with invalid recipient addresses that we 
> should reject outright at the HELO phase, and these messages 
> will have to be bounced later if the sender retries.  
> Further, if we're front-ending other servers, we may not even 
> know whether the user address is valid.
> 
> But ... if the internal servers (including a dummy server on 
> the relay box for access_db checks) supported VRFY, then MdF 
> could check the addresses early on by first consulting the 
> internal server(s).
> 
> Make sense?

Yeah, that does make a lot of sense, and it's probably doable, but I've
found that it's simpler to just extract all of the valid addresses from the
internal server with a cron job, then build an access.db for the front-end
server to use.  This allows you to reject the bad addresses at MTA level, so
that you don't even need to invoke MdF.  I'm using Sendmail, but I imagine
this would work with other MTAs as well.

Here are a couple of different approaches to this issue:

http://www.mimedefang.org/kwiki/index.cgi?RelayCheckAddresses
http://www.mimedefang.org/kwiki/index.cgi?Exchange2Access

I use the second technique.  Just remember that you need to add:

to:yourdomain.com       ERROR:5.1.1:"550 User unknown"

to the beginning of your access database, so that the server will reject
everything that doesn't match a valid recipient address.

Brian Leyton
IT Manager
Commercial Petroleum Equipment