Attach list of files and email using secure connection
In general, the code looks good.  I just have a few miscellaneous remarks.

Code organization


Function names should be named lower_case_with_underscores by PEP 8.
I would split the message composition and sending into separate functions.
It is good practice to avoid embedding passwords into your source code.  I suggest storing the account information in a YAML file, or at least as constants in a separate Python module.
The parameters are hard-coded, so the function is of limited utility.  The function could accept parameters with defaults:

def compose_email(from='sender@example.com',
                  to=['recipient_1@example.com','recipient_2@example.com'],
                  attachments=[])
    …

def send_email(msg, username, password)
    …



Mail content


The MIME type for .xlsx files is application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.
Concatenating file paths using os.path.join(lpath, item) would let you not have to worry about the path component separator.  Personally, I would choose to pass full paths to the function instead, to avoid assuming that they are all in some hard-coded directory:

def EMAIL_FILES(attachments):
    …
    for path in attachments:
        with open(path, 'rb') as f:
            part = MIMEBase('application', 'vnd.openxmlformats-officedocument.spreadsheetml.sheet')
            part.set_payload(f.read())
            part.add_header('Content-Disposition',
                'attachment; filename="%s"' % os.path.basename(path))
            Encoders.encode_base64(part)
            msg.attach(part)
    …

EMAIL_FILES([os.path.join('C:/Path/to/my/excel/files/', f) for f in
    ['excelfile_1.xlsx', 'excelfile_2.xlsx']
])

I'm puzzled by why you defined body as a list of strings, only to join them all into one long string.  If the body contains non-trivial content, consider writing it as a """longstring""".  Also, you may need to encode the MIMEText using Encoders.encode_quopri().