ISPs blocking SMTP connections from dynamic IP address space

Nicole nicole at
Wed Aug 6 13:19:20 PDT 2003

On 06-Aug-03 Unnamed Administration sources reported Doug Poland said :
> On Wed, Aug 06, 2003 at 11:41:56AM -0700, Nicole wrote:
>>  Yes I too have resorted to blocking Ip's with no reverse DNS and
>>  its amazing how many big companies can fall into this. 
>>  As to the Dynamic Space, I also block DSL/dynamicly assigned Ip's
>>  as I fall aware of them. (See Example below) Since some Isp's are
>>  smart enough to identify their dynamicly allocated space it makes
>>  it easy.  So far it is extreemly rare for someone to be sending
>>  mail directly from these DSL/dynamic spaces that anyone wanted to
>>  recieve. 

> except those of us running FreeBSD SMTP servers from broadband
> connections with valid reverse DNS

 Those who do so should be doing one of the following.

a) Since you must be using dedicated IP space, have proper DNS setup.
 Pacbell for example will change your reverse DNS for free to match the forward
name you assign to your server. (thus solving two problems at once)

b) Set your server to relay mail via your IP providors server or some other


> -- 
> Regards,
> Doug

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