ISPs blocking SMTP connections from dynamic IP address space

Vince Hoffman Vince.Hoffman at
Fri Aug 8 03:45:26 PDT 2003

1) ask your isp to set it up as they probably control reverse dns for your
IP-address block (all they will need is IP and fully qualified hostname) (a
whois on your IP will probably tell you who controls it or which database to
look in to find out.)
2) If you have been delegated control of reverse dns for your IP range, set
up the relevant PTR records, if your running a DNS server and have this then
you probably know how to do this already.

Ironicly this probably wont get to the list because my companys ISP is being
very slow at delegating reverse DNS for our range to us, so we currently
have no reverse DNS.


> -----Original Message-----
> From: Bruce Pea [mailto:pea at]
> Sent: 07 August 2003 13:50
> To: questions at
> Subject: Re: ISPs blocking SMTP connections from dynamic IP address
> space
> Since we began blocking servers with no reverse DNS we've 
> been amazed at 
> how many mail servers are setup with no reverse DNS. We've 
> had several 
> instances where we've been asked by the party being blocked 
> how to fix 
> the problem. Since I'm not a DNS expert all I've been able to 
> tell them 
> is to fix their DNS entry so they show up when we do an 
> nslookup on them, 
> which isn't very helpful but is about all I know to say.
> It would be very useful if someone could explain or give 
> instructions on 
> how to fix this problem so we all could pass the info along 
> to people who 
> need to straighten out their DNS.
> Does anyone have a document explaining such things handy they could 
> share??
> bp
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