php email filter not working(?)

I happily use this plugin on a number of sites – one where the cache fills very fast (not the issue for this post). My client was getting spammed with warning messages (I note the excessive warnings has been fixed) so I searched on how I could get the warnings sent to me as I maintain the site.

so I found
add_filter(‘autoptimize_filter_cachecheck_mailto’, ‘[email protected]’);

to drop into my child theme functions.php

– yes – I did use my email address

Autoptimize is still maxing out quickly but no warnings are arriving in my email box (or junk)

Rather than having to hunt down the filter which is not successful for me I was wondering if a change of email address, for cache warnings, could be a feature in the settings.