Stupidest thing :o ...
This was failing:
ini_set('smtp', 'mail.isp.com');
mail('a@b.com', 'test', 'test', 'From:d@e.com');
This worked:
ini_set('SMTP', 'mail.isp.com');
mail('a@b.com', 'test', 'test', 'From:d@e.com');
PHP version 5.2.0
Mustve spent at least two days trying to figure this one out.😃 😃