Well, I think I solved it.
I ADDED the path to the PEAR foler in the php.ini file such
include_path = ".:/bitnami/lamp71stack-linux-x64/output/php/lib/php:/opt/bitnami/php/lib/php:/opt/bitnami/frameworks/smarty/libs"
pear config-get php_dir
in Putty to find my path.
Note, there are three include paths in that, sparated by :
I still cant send mail but at least Im getting the sort of errors you might expect with a remote mail server, 550 errors etc.