auth_string = 'user=%s1auth=Bearer %s11' % (email, access_token)
imap_conn = imaplib.IMAP4_SSL('imap-mail.outlook.com')
imap_conn.debug = 4
imap_conn.authenticate('XOAUTH2', lambda x: auth_string)
imap_conn.select('INBOX')
print(imap_conn.list())

{ 'access_token': '****',
  'scope': 'User.Read Mail.Send Mail.ReadWrite',
  'refresh_token': '***',
  'token_type': 'Bearer',
  'ext_expires_in': 0,
  'expires_in': 3600
}

46:15.27 > b'JEKB1 AUTHENTICATE XOAUTH2'
46:15.57 < b'+ '
46:15.57 write literal size 1584
46:21.21 < b'JEKB1 NO AUTHENTICATE failed.'
46:21.21 NO response: b'AUTHENTICATE failed.'