Outlook not connecting to Exchange 2013

Hi Technet,

We're using outlook 2010 and it can't connect to Exchange server 2013. It was working fine just two days ago and now it stopped working, several users are reporting this issue and I don't know whether the number will increase later.

I have tried reconfiguring it but it still can't connect. I can ping the mail server but it can't connect to the exchange

any help please !!!