have been through configs and FAQs and mailing lists way too many times in the past couple days, seeking only to find the answer to this question:
Is it at all possible to disable *all* rdns lookups for smtp sending?
It doesnt seem to me like this helps with security at all, in fact it just causes more trouble than its worth. We run email for quite a few companies, and none of them have rdns entries because they simply dont need it.
I have setup Exim with qpopper-sql so that it requres a valid user to check their mail before being allowed to use the smtp service. This part works great, and the user's ip address gets entered into the databgase. however, exim fails the comparison every time, deciding right off that since the ip didnt reverse, it isnt valid. It doesnt even *try* to get the list of ip addresses from the database unless it reverses. Note, however, that it does work correctly if the ip reverses, and goes to to use the database to devide if relaying is allowed.
In the process of trying to drebug this, I tried every configuration and debug that i could find. The only thing that seemed to make a difference was adding +warn_unknown to host_accept_relay (before mysql;MYSQL_RELAY, it made no difference if put after), and this just made it into an open relay, seeming to take the fact that it didnt resolve as all the reason it needed to continue.
So, does anyone have any idea why the mysql;MYSQL_RELAY forces a dns lookup, or how to stop it from doing so? the sql query is only supposed to return a list of ip addresses, and i assume it is doing so, but i have no way of knowing for sure.
Any help is appreciated.
