Brother MFC-5440CN - Manual (Page 57)

3 - 6 SETUP SEND
Out of Memory message
If you get an Out of Memory message while scanning the first page
of a fax, press Stop/Exit to cancel the fax. If you get an Out of
Memory message while scanning a subsequent page, you will have
the option to press Black Start to send the pages scanned so far,
or to press Stop/Exit to cancel the operation.
If the memory is full and you are faxing a single page, it will be
sent in real time.