DNS causing problems with sendmail?

[Drew J. Weaver]

Hi, I've had this problem for a few days now, we have a small dial-up ISP and when users dial into one of our cities they get a 209.xxx.xxx.xxx IP and our mail server responds normally, we have another modem pool in that city that consists of 206.xxx.xxx.xxx IP addresses, if a user gets a 206.xxx.xxx.xxx IP address and they attempt to check mail it takes a good 2-3 minutes before the sendmail connection starts, which is an obvious problem because of the timeouts on email clients (and.. 2-3 minutes is just bad). I've been kinda asking around on comp.mail.sendmail about this issue and they are telling me it is a DNS problem. Well, I know that my mail server can reverse the IP addresses because if I am logged in and issue a host command with the IP after it the server is able to produce the proper reverse name. Another user thought it was because I have no Forward dns (a record) for what the IPs are reversed to, but the fact is I've NEVER had any A records or anything for my modem pools. I also have another server running the same version of sendmail, and if I dial into this city and get a 206.xxx.xxx.xxx IP and telnet to port 25 on that server it comes up instantly. So this appears to be an issue only effecting one daemon on one server. The afflicted server also runs a POP daemon that isn't having any problems of this type.   Does anyone have a clue on this? I'm awfully confused at this point.   Thanks, -Drew