If you send a compressed file with the php or other codes in it, Gmail may reject the attachment due to security and attachment guidelines. You may receive the following message:

Your message did not reach some or all of the intended recipients.
Subject: Emailing: XXXX.zip Sent: 2/14/2010 1:15 PM
The following recipient(s) could not be reached: ‘XXXX XXXX’ on 2/14/2010 1:15 PM 552 5.7.0 review our attachment guidelines. 20sm5501368iwn.13

It apparently shows that the attachment was sent as a zip file. Gmail is able to check the content of the email if the attachment is compressed in zip format.

The solution of this is to send the same attachment as a rar format. Gmail is not able to check the content of the attachments compressed with WinRAR so, you should have no problem to transmitting the file to the recipient.