[ad_1]
Hi Bruno,
That mailster.co is a premium plugin so I cannot be sure without seeing the rest of the code in that file. If it is only the one ini_set that is highlighted then Yes, this is probably a False Positive. I have updated the definitions for this threat and, if the code is just as you say here, then it will not be flagged as a know threat any more.
If you have any further troubles with this after downloading the latest definition updates then please send me a copy of the whole file so that I can address the issue more completely.