g4gmail_markAsRead will mark the specified message as read. This will also update the G4GMHLPF file with the updated labels list for this message. This is called internally by the g4gmail_listMessages procedure.
Returns: 0 for success or -1 for error.
Error Message (output) - Error message
Settable Variables (use g4gmail_setValue):
id (required) - Your Google ID
message_id (required) - The message ID of the message to mark as read.
ccsid - The CCSID to use. The default is 1208.
debug - Specify *YES to turn on debug, or *NO to turn off debug. The default is *NO.
debug_file - Specify the fully qualified file name for the main debug file. The default is /tmp/g4g_[msgid]_markAsRead.txt.