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(?) Exim with Dynamic IP - 2 Questions

From Balbir Thomas

Answered By: Neil Youngman

Dear Answer Gang,

I am using exim to deliver mail form my local host. I have a dynamic IP address and am using zoneedit as my dns server. So mail to my userID@my.domain is delivered straight to me. However I have trouble sending mail to certain address as their ISPs/Postmasters have decided to block emails originating from dynamic IP address to reduce spam. For example AOL. I would be greatfull if you could suggest means to solve this problem, short of paying for a static IP (which I don't need but for this reason). Talking to my ISP (RoadRunner) has been a waste of time.

(!) [Neil] It's certainly possible. The Exim FAQ at http://exim.org/exim-html-4.30/doc/html/FAQ_3.html has an example of setting up routers to send local mail to hosts on the local network and everything else to a smarthost. this should be easy to adapt to do what you want.
If all else fails read the documentation. The Exim documentation, though large, is very informative. You just need to read it selectively and pick the relevant chapters.

(?) My second question is how to set up postmaster at my local host. My current exim config accepts mail sent to postmaster@my.domain however it does not accept mail to postmaster@dhcp-xxx-xxx-xxx-xxx.columbus.rr.com which is my hostname assigned by my isp. The xxx being the ip address which can change. Is there a way to make exim accept mail sent to this email address such that the ip address (i.e. in this case domain name) part is updated automatically.

(!) [Neil] I don't know about getting it to update the address automatically, but you can have it match a pattern like postmaster@dhcp-*.columbus.rr.com on the basis that it's unlikely anyone else's postmaster mail will be directed to your IP. Frankly I wonder who would send postmaster email to an address like that anyway.
In the default exim 4 config this is accepted by the rules:
  domainlist local_domains =@

  accept  local_parts   = postmaster
          domains       = +local_domains
According to the documentation '@' ... 'is a special form of entry which means the name of the local host, so this should normally match, but I guess your system is set up to use "my.domain" as the hostname, instead of the RoadRunner host name.
As an alternative, it may be that adding dhcp-$interface_address.columbus.rr.com or some variation thereon to local-domains will achieve what you want. I have not tried this, so I can't be sure it will work. If you try it, be sure to let us know whether it worked.

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Published in issue 108 of Linux Gazette November 2004

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