On Wed, 16 Oct 2024 at 14:30, Bill Cole via Postfix-users < postfix-users@postfix.org> wrote:
> On 2024-10-16 at 09:05:09 UTC-0400 (Wed, 16 Oct 2024 14:05:09 +0100) > Dominic Preston via Postfix-users <lzq...@gmail.com> > is rumored to have said: > > When sending email via my email client, there is a delay of about 5 > seconds > before the email sends. I believe this is as a result of my ISP's DNS > servers being unresponsive when responding to PTR record lookups for my > client IP address. > > If your rDNS is non-performant or non-existent, you probably should find a > better hosting provider. > It not the DNS servers of my hosting provider, it's the DNS servers of the company providing me with an internet connection. They are the ones operating the servers responding to PTR records for my email client's IP address. However, multi-second delays at connect time are perfectly normal and > intentional in many cases. For example, Postfix's postscreen component will > pause for 7 seconds at connect time in the middle of the intro banner for > IPs that are not in its cache of non-spambot clients. > Understood, although when clicking "Send" on a tiny email, it's something of an irritant to be looking at the sending bar for several seconds before it actually sends. > Is there any way to disable PTR record lookups for a given set of > IPv4/IPv6 > addresses? > > On your own mail server, the canonical mechanism to short-circuit rDNS > lookups is to add entries in the hosts file for the IPs needing the faster > resolution, assuming that you have your system resolver set to use files > first (in /etc/nsswitch.conf) > Unfortunately modifying the hosts file isn't going to work, I use IPv6 with temporary addressing, so I'd need to add billions of addresses to the hosts file, or use a solution with a subnet mask.
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