clients of certain isp cannot connect to my sites

[hotwired]

Hi
I have a problem which I'm sure is common, it just has to be! Here's the specs of the problem, numbered so I don't forget anything:
1. I have a managed dedicated server ip 66.195.19.200 where I have all my sites hosted.
2. One particular isp prexar.com cannot resolve anything at that ip. Neither anyone that works there nor their clients connected to the isp can view my websites nor engage in any email in or out with my client's sites hosted on my server. i.e. if my clients are using their website as smtp and pop they cannot engage in email with any clients of prexar.com isp.
I think that's it. my nameservers are squeaky, I have rDNS, we're down to it being a router or network issue but the isp has informed me that it cannot be them, and I tend to believe it as they have checked everything. Does this sound familiar to anyone?? What are the possibilities os I have some "ammo" for either my web hsoting provider or the isp in question??

[sorted]

Hi
I have a problem which I'm sure is common, it just has to be! Here's the specs of the problem, numbered so I don't forget anything:
1. I have a managed dedicated server ip 66.195.19.200 where I have all my sites hosted.
2. One particular isp prexar.com cannot resolve anything at that ip. Neither anyone that works there nor their clients connected to the isp can view my websites nor engage in any email in or out with my client's sites hosted on my server. i.e. if my clients are using their website as smtp and pop they cannot engage in email with any clients of prexar.com isp.
I think that's it. my nameservers are squeaky, I have rDNS, we're down to it being a router or network issue but the isp has informed me that it cannot be them, and I tend to believe it as they have checked everything. Does this sound familiar to anyone?? What are the possibilities os I have some "ammo" for either my web hsoting provider or the isp in question??

Could your dedicated server provider have a firewall rule set to block access to a prexar IP address block?

I dunno what mail server software you are using but if prexar clients can't send mail to you then have you checked that you don't have their mail server IP's listed in your Mail Server Software's Open Relay Blacklist? MDaemon v5 and v6 (I think) used serveral defunct blacklists so were wholly unreliable.

Just suggestions, the first think I would do is get an account with one of these troublesome ISP's and test things for yourself, try some traceroutes, check their DNS entries etc.

I once had a similar problem and (whilst I think its unlikely in your case) Before I went dedicated and began running my own Name Servers, my previous host forgot to remove the entries in their DNS, so when customers using their service wanted to email me, their mail was routed to my old mailbox. This problem reoccurs every now again with our own customer, when a client leaves without cancelling their account. Worth checking though.

[Essentials]

Accidental double post :)

[Essentials]

Only listed at a couple of place for spam that I see:

http://dnsstuff.com/tools/ip4r.ch?ip=66.195.19.200

May want to check the mail settings and be sure it isn't a local ISP issue or other issue with the ISP vs the ip address you have listed.

Also, if it appears to be an ISP issue try to change your outgoing email settings to your ISP's and keep your incoming as your servers mail settings. This can bypass the ISP listing or your current ip address listing if need be (your ISP won't block out their own email most likely).

Also, your ISP or your current datacenter (provider) may be blocking out the ip address alltogether - this can only be resolved by them so have them check their current server settings.