Mail_Mbox will insert the message according to the specified offset.
(Remember: message 3 is the fourth message). The default is to insert
the message AFTER the last message (offset = null).
Note: Mail_Mbox automatically adds \n\n at end of the message.
Parameter
string
$content
The content of the new message.
mixed
$offset
Return value
returns
Return true or the PEAR_Error object on failure.