Generally major email service providers like hotmail and yahoo do rate limiting so that they can protect their customers from being spammed.

The above error message indicates that there have been too many mail connections to hotmail.co.uk from qatar.net.qa, hence this has made hotmail.co.uk suspicious that the domain/IP qatar.net.qa may be indulging in spamming.

there is nothing that you may be able to do, its the administrators of the domain qatar.net.qa will have to contact hotmail to get the IP/Domain delisted