Postfix Address Verification

[Drew Marshall]

On 27 Jun 2007, at 03:12, Seamus Allan wrote:

> Gareth wrote:
>> See
>> http://www.mailscanner.info/wiki/doku.php? 
>> id=documentation:configuration:mta:postfix:how_to:reject_non_existent 
>> _users
>> Thats what I do and it works very well.
>>
>> Just make sure Exchange is configured to reject mail to unknown
>> recipients. If you cant do that then there are other ways such as  
>> using
>> LDAP to regularly pull out a list of valid addresses from exchange,
>>
>> On Mon, 2007-06-25 at 23:24, Jody Cleveland wrote:
>>
>>> Hello,
>>>
>>> I've got a RedHat 5 server with Postfix and MailScanner. This  
>>> server checks
>>> all incoming mail and then forwards it on to an Exchange server.  
>>> I'm looking
>>> for a way to verify recipients without touching active directory.  
>>> Will
>>> either of these work at all?
>>>
>>> smtpd_recipient_restrictions = reject_unauth_destination
>>> smtpd_recipient_restrictions = reject_unverified_recipient
>>>
>>> - jody
>>>
>>
> I am curious about this; it seems to make very good sense to do  
> this (and will in fact cut down the number of bounces created by my  
> mail gateway MailScanner machine), but I wonder how much more work  
> has to be done by Postfix to accomplish this.

It's a lot less than trying to keep running the mail queue that's  
full of undeliverable bounce notifications. Reject unknown recipients  
at SMTP stage will mean that you don't have to use your bandwidth to  
download the full message, process it through MailScanner &  
SpamAssassin, deliver or attempt to deliver somewhere else, create  
the bounce notification and attempt to deliver this bounce using your  
bandwidth. If it's not deliverable then keep retrying for x number of  
days and re-examining the message in the queue to work out when it  
must keep trying.

In comparison any form of db look up from hashed file to SQL or LDAP  
is really cheap. Couple that with one or two other tricks such at  
proxying for SQL for example (To retain connections) and you really  
have very little overhead at all. In fact there are other checks that  
are more work, such as RBL look ups that are much more work.

Drew
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