Upgrading PHP from Version 4.X To 5.2 isssue with include_once("Mail.php");

[Donn]

Hello, all.

Recently, I've been upgrading all of my carts, from various versions, from 1.3.7, to 1.3.8A, to 1.9H.

On my server set to PHP 5.2, almost everything works.

I added a few things that were custom, and porting them to the newer version has me stumped.

One such change sent out mails, but not via the ZENMail functions within the cart. (I had my reason for this!)

But now, I get an error message when trying to use the same statement that worked in PHP 4.X:

include_once("Mail.php");

I now get get this error msg with PHP 5.2:

Warning: include_once(Mail.php) [function.include_once] failed to open stream. No such file or directory in my/path/t/o/f/i/l/e/s
Warning: include_once() [function.include] Failed opening Mail.php for inclusion include_path="./usr/local/php5/lib/php


Is this not valid for PHP 5.2?
What should I use instead???