SELECT m.*,
  CASE m.senderuserid
    WHEN '2'
    THEN 'Server'
    ELSE concat(u.voornaam,' ',u.famnaam)
  END AS fname,
  u.id
FROM (`user` u, `message` m)
WHERE (m.senderuserid =u.id || m.senderuserid ='2')
AND m.customercode   ='test'
AND m.archive       != '1'
AND m.customercode   ='test'
AND m.receiveruserid = '4e4d8a4dd886e4.43611321'
AND m.type          IN ('info','action','permission','reminder')
AND u.customercode   ='test' ORDER BY datecreated DESC;

--> 2 seconds