Reject mail from invalid domains

[Hugo van der Kooij]

On Tue, 29 May 2007, Jorge Costinha wrote:

> invalid domain, are domains that cannot be resolved by DNS. i belive it is a 
> good practice to reduce spam and workload of mailscanner and spamassassin if 
> mails coming from invalid domains are block. am i right?

There are a few scenarios.

You ask for the domain name but get a clear answer it does not exist ==> 
No need to receive it as it is bogus email

You ask for the A and/or MX records and find that none of these exist ==> 
Again no ways to delivere them messages so why accept theirs?

You ask for it but can not get an authorative answer ==> Tell them to get 
back later and try again.

You can additional checks and see how well they hold out.

Fighting spam is a balance of costs. Money is only part of the 'costs' one 
has to take into account. And not all of us value costs the same way so 
different persons may get to different results.

Hugo.

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