Description:
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I am currently running PHP5 with Apache 2.0.49 and an open-source shopping cart solution OsCommerce (www.oscommerce.com).  The OsCommerce email function is a standard one (I won't paste here) that sends standard or MIME emails depending on what you choose for it to send.  Running PHP 4.3.1 I had no issues sending email, however after successfully upgrading to PHP5, I now receive an error.

As I said, the email function is nothing deviating from most of the general working functions posted on the web.  My php.ini lines that it would be referring to are below (edited out my domain name):

[mail function]
; For Win32 only.
SMTP = mail.mydomain.com
smtp_port = 25

; For Win32 only.
sendmail_from = myemail@mydomain.com

Reproduce code:
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The specific line the error below refers to is here:
return mail($to_addr, $subject, $this->output, 'From: ' . $from . $this->lf . 'To: ' . $to . $this->lf . implode($this->lf, $this->headers) . $this->lf . implode($this->lf, $xtra_headers));

The entire email function is here:
http://www.modsp.com/email.php.txt

Expected result:
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Emails are processed and sent to recipients.

Actual result:
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Warning: mail() [function.mail]: "sendmail_from" not set in php.ini or custom "From:" header missing in \path_to_storefront\email.php on line 500

(edited out full path to storefront)