SMTP connection problem for drupal 5; drupal 6 implementation

My hosting provider updraded their servers and it broke the mail function in my drupal 5 implementation. The hosting company says it is a drupal problem even though they broke the function. The website also needs to be upgraded, but the original develop customized many of the files. I would like to fix the mail function as soon as possible, and then upgrade the site over time. The website is at http://www.lexpertise.com/

If you can help email me at lexpert@lexpertise.com. Please indicate your rates and availability.