Mass Mailer only works with CURL code removed

I have the civicspace 8.5 version of mass mailer installed on four sites on a server with PHP running as a CGI.

It only works if you replace the CURL code in phplist.module with the the original shell exec code, even though CURL is installed on the server:

If you get rid of the curl code it works fine.

This strikes me as odd, because I thought the CURL code was introduced in order to get massmailer working on servers that have PHP running as a CGI?

The older versions of massmailer 4.6 and phplist 2.9.4 wouldn't run at all on php/cgi server without some code alterations in several spots.

But now it seems to work *almost* out the box, except you have to remove the new CURL code and replace it with the older shell exec.