The PHP mail() function is working on your server, Chopin. I just tested it.
Check spam folders in your "To" accounts and for returned messages in your "From" accounts.
They have to keep tweaking the system because of all the people who come here and use their free accounts as spam vehicles.
Is this a CMS (Joomla, SMF, etc) that is having problems or a standalone script? If you could post the script in question, we might be able to give you some things to try.