Hello Gilles,

Thank you for your response.

With regards to the question about negating ‘rdns’, can I explain how I 
understand it and maybe you can confirm either way.

Using the example,
        filter f01 phase connect match !rdns disconnect "550 missing rDNS"

On connection (connect) we check (match) if reverse dns is invalid (!rdns) and 
if so then disconnect the session. For invalid, this would mean no reverse dns, 
or an incorrectly configured reverse dns. 

I did read the man page about ’smtpd.conf’, more so about filters and wanted be 
sure I comprehend it. 
 
Thanks

Nino


> On 4 Jan 2020, at 11:07 am, gil...@poolp.org wrote:
> 
> January 4, 2020 12:25 AM, "Antonino Sidoti" <n...@sidoti.id.au> wrote:
> 
>> Hello,
>> 
> 
> Hello,
> 
> 
>> I have some basic questions about filters?
>> 
>> What do we need to negate the rdns for the following command?
>> 
>> filter f01 phase connect match !rdns disconnect "550 missing rDNS”
>> 
> 
> I'm unsure I understand this question, the example you show negates rdns,
> this is what I use myself to junk incoming sessions without rdns.
> 
> 
>> Can someone please explain the difference between reject and disconnect when 
>> used in a filter?
>> 
> 
> Very simple.
> 
> When you use `reject` the command is rejected but the session isn't 
> disconnected.
> If a client had multiple mails for you, rejecting a mail can allow it to 
> submit a
> different mail before it gets disconnected.
> 
> When you use `disconnect` the client gets disconnected after the rejection, 
> so it
> has to connect again.
> 
> 
>> Many thanks
>> 
>> Nino
> 


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