Error message

Hi,

I’m trying to setup the plugin, but when I want to test my settings it says ‘The extension imap.so can’t be loaded, please change your PHP configuration to allow or use the POP3 method without IMAP extension” (Translated from Dutch)

Any idea what causes this message? I have tried setting it as both IMAP and POP3, with and without SSL. With all settings I get the same message.