A White ipfilter is an another ipfilter file, an addition to the ipfilter feature which prevents specific IPs to be banned even if they already exists the main ipfilter.dat file.
If you have to create this file manually and add ip number you want to block with an editor in the file in the config directory
Added by Stulle, since MorphXT v11.2
ADD: IP Filter White list [Stulle] IP Filter White List: + IPs on this list will not be banned + use "ipfilter_white.dat" to add IPs to the White List
-  eMule docs how to find the config directory