Blocking emails that claim to come from our

Dhawal Doshy dhawal at NETMAGICSOLUTIONS.COM
Wed Dec 7 11:51:23 GMT 2005

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Drew Marshall wrote:
> On Wed, December 7, 2005 10:43, Glenn Steen wrote:
>>On 07/12/05, Erick Perez <eaperezh at> wrote:
>>>what about MS and postfix?
>>>where do i implement that?
> The only thing I would add is that sometimes helo rejection can be too
> harsh (There are loads of Exchange boxes that have strange AD domains
> setup due to AD getting confused over internal and external DNS and end up
> heloing with something like exchange.domain.internal which will be
> rejected with 'reject_invalid_hostname') so you might chose to add
> 'warn_if_reject' in front so you just log these and take a view on
> rejection based on your hits (Like your best customer won't be rejected
> for example!).

minuscule correction

'reject_invalid_hostname' under 'smtpd_helo_restrictions' will simply 
reject the 'helo' if it contains any special / bad characters..

The parameter you are talking about is reject_unknown_hostname, which 
will reject the mail if no valid A/MX record exists for the helo 
hostname and causes quite a few false positives.


- dhawal

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