What is an Exim iplsearch file?

Introduction

Sometimes you will want to have Exim search for data but you don't want that stored in the exim.conf file. You can use a file for this and then manually create a file with your list of data.

For example this may be in your exim.conf file:

smtp_accept_max_per_host = ${lookup{$sender_host_address}
iplsearch{/etc/mycustomfile}}

You can create mycustomfile with the data and it will be read by Exim.

The structure of the data within the file has a specific format:

key: data 

The key for an iplsearch lookup must be an IP address (without a mask). The file is searched linearly, using the CIDR masks where present, until a matching key is found. The first key that matches is used; there is no attempt to find a "best" match.

For further information please review the Exim documentation.

https://www.exim.org/exim-html-current/doc/html/spec_html/ch-file_and_database_lookups.html