Drupal expert required - Drupal not sending emails

Tonight i have had a server admin reinstall php, we have tested that the server sends mails correctly but we have one drupal installation that will not send emails out at all. I have installed an smtp module to see if i could work around this problem but that does not work either. There is something that is stopping this Drupal [login to view URL] version from sending mails and i need someone who is very familiar with drupal to sort it out for me quickly and without drama. Please no people bidding who think they can solve this with server. The Drupal install needs fixing, also we will not be upgrading drupal to [login to view URL] either as we are sure the custom files will not work with 7.xx. We need someone to fix this install, as it is now to send out emails properly. First person to convince me that they can fix this, and straight away, until completion will be given the work.