[Mimedefang] syntax for the filter command?

[James W. Curtis]

using the example filter in the heartlight graph,
'filter'       => '^(?:(?!westover.org).)*$',
What is the syntax for matching the domain that you want to see?
'filter'       => '^(?:(?=mydomain.com).)*$',
does not work.  I'm obviously not a programmer, where can I find info?


Have mercy, I'm a network guy in a programming world.
James William Curtis