Hi,
I had problems with sendmail under PHP on my Mac OS X machine. I use EIMS (Eudora Internet Mail Server) 3.2.x, an excellent Mac OS email server, which, naturally enough, takes over port 25 for SMTP. I had to find a way to use EIMS for web forms (and other applications) where email was necessary. BTW, this uses the Abyss PHP 5 package for Mac OS X. This may not be the most elegant solution ever, but it works.
First, I chose PHPMailer and downloaded the package. I installed the two class files (class.phpmailer.php and class.smtp.php) in the HD/Applications/PHP5/lib/php/ directory.
I then created an email address (let's call it forms@host.com) with login enabled and the world's nastiest password. I would also suggest you limit, if you can, relaying for the domain to LAN IP Nos and/or local domains only.
I especially wanted custom form response pages for this install, as I hate the cheap looking things that PHP generates automatically. I wanted pages that look like the website they came from.
OK. So here's the code for the PHP:

<?php
// Ian McPherson - third go 14-06-07

$title = $_POST['title']; // form field
$firstname = $_POST['firstname']; // form field
$lastname = $_POST['lastname']; // form field
$company = $_POST['company']; // form field
$address = $_POST['address']; // form field
$code = $_POST['code']; // form field
$state = $_POST['state']; // form field
$country = $_POST['country']; // form field
$email = $_POST['email']; // form field
$phone = $_POST['phone']; // form field
$fax = $_POST['fax']; // form field
$request = $_POST['request']; // form field

$ian_err = "error.html"; // html error page
$ian_ok = "thanks.html"; // html thanks page

require("class.phpmailer.php"); // call to PHPMailer class file

$mail = new PHPMailer(); // make new email message

$mail->IsSMTP(); // telling the class to use SMTP
$mail->Host = "0.0.0.0"; // SMTP server IP - LAN IP is OK
$mail->From = "forms@host.com"; // genuine email address in SMTP Server - login must be on
$mail->AddAddress("client@client.com"); // final TO address

$mail->Subject = "Your favourite project has had an email response";
$mail->Body = "Dear Brian,\n\nYou have received a Brochure request from the free\nbrochure page on the Your Favourite Project website.\n\nThe enquirer's details are as follows: Brochure request\n\nPlease post to:\n\nTitle: $title\nFirst Name: $firstname\nLast name: $lastname\nCompany: $company\nAddress: $address\nPostode: $code\nState: $state\nCountry: $country\nEmail: $email\nPhone: $phone\nFax: $fax\nAny additional comments: $request\n\nRegards,\n\nFred Nerk\nYour Favourite Project Webmaster\nmailto:fred@host.com"; // body of email - \n is a line break, $xxxxx are form fields to be included in the email

if(!$mail->Send()) // send the email to the SMTP Server
{
   header("Location: $ian_err"); // if there's an error, send browser to this page
   exit;
}
else
{
   header("Location: $ian_ok"); // No error? send browser here
}
?>

Now, here's the code for the Javascript form trapping. Note that not all fields are "required":

<SCRIPT>
<!--  Hide from old browsers

function checkForm(form)
{
	if (form.title.value == "")
	{
		alert("Please enter your Title.");
		return false;
	}

if (form.firstname.value == "")
	{
		alert("Please enter your First name.");
		return false;
	}

if (form.lastname.value == "")
	{
		alert("Please enter your Last name.");
		return false;
	}

if (form.company.value == "")
	{
		alert("Please enter your Company name.");
		return false;
	}

if (form.address.value == "")
	{
		alert("Please enter your Address.");
		return false;
	}

if (form.code.value == "")
	{
		alert("Please enter your Postcode or Zip.");
		return false;
	}

if (form.state.value == "")
	{
		alert("Please enter your State.");
		return false;
	}

if (form.country.value == "")
	{
		alert("Please enter your Country.");
		return false;
	}

return true;
}
// -->
</SCRIPT>

The last thing to do is add the Javascript to the FORM tag in your HTML:

<FORM ACTION="whatever.php" METHOD=POST onSubmit="return checkForm(this);">

Obviously, the problem with this approach is that every form page requires an individual script.
Yeah, I know. That's a time-wasting bummer...
Maybe some genius PHP guy can figure out how to rewrite or extend this approach to "include" text from an external file, which would make the script form independent? Now that would be excellent...
Any good ideas, you guys? I'm all ears... :)
Ian McPherson