How to get raw email data with the imap extension?

I'm looking for a way to download the whole raw email data (including attachment), similar to what you get by clicking "Show Original" in Gmail.

Currently, I can get the raw header and some parts of the mail body by this code:

$this->MailBox = imap_open($mailServer, $userName, $password, OP_SILENT);
...
$email->RawEmail = imap_fetchbody($this->MailBox, $msgNo, "0");
$email->RawEmail .= "\n".imap_fetchbody($this->MailBox, $msgNo, "1");

Also I know that changing the 3rd parameter of imap_fetchbody might return the encoded attachment. Guess I need a loop here to get the raw email part by part, but what's the condition to stop the loop?

Is there an easy way to get the whole email at once?

Any help would be appreciated.

Solution

My answer is "overcomplete", see Boy Baukema's answer for a more straight forward "view source" way of doing if you don't need the whole structure of the email.

If you want to fetch all, you need to fetch

The headers imap_fetchheader.
Obtain the number of bodies the message has imap_fetchstructure.
Each mine-headers a body has imap_fetchmime.
Each body it has imap_fetchbody.

As mime-message can have multiple bodies, you need to process each part after the other. To reduce load to the server use the FT_PREFETCHTEXT option for imap_fetchheader. Some example code about imap_fetchstructure in another answer that shows handling the imap connection and iterating over parts of a message already through encapsulation.