friends we have few accounts which we dont want to be accessed outside LAN or domain joined computers. no ECP no OWA outside corporate network. how can we do this.

secondly how can we know that how many devices are connected to a particular email account via outlook/ OWA or mobile. as we are suspecting that there is a account which is getting accessed from outside and i want to know who is accessing that.. the best best is to know which device is being used .. computer name or device ID. with IP and other relavent information. so can we get all the device information connecting to that e

Hi,

According to your description, I understand that you want to restrict some account access Exchange server from external.
If I misunderstand your concern, please do not hesitate to let me know.

We can disable relevant feature for special account, for example OWA, IMAP, ActiveSync. And we can disable all external internet access by reconfigure virtual directory.  Thiss not your want.
However, we can do more configuration to achieve your expectation. I find an similar thread about your requirement, for your reference:
https://social.technet.microsoft.com/Forums/en-US/e2825ae4-8140-4a2a-baaa-4d402c87f33a/restrict-owa-and-outlook-anywhere-access?forum=exchangesvrdeploylegacy
https://social.technet.microsoft.com/Forums/office/en-US/e03da1ae-790b-4a2d-8bd6-878d1376406c/exchange-2013-owa-restrict-external-access-to-owa-while-keeping-internal-access-open?forum=exchangesvrclients

If you want to get more details about client information, we have to look over IIS log. More details please refer to:
http://blogs.technet.com/b/karywa/archive/2013/04/21/getting-started-with-log-parser-studio.aspx

Thanks

Just want to add some additional information    go to recipients=>mailbox=> click the user mailbox-> on side you can see mobile device=> their you can disable ow and active sync of particular user additional click view details, there you can see the device associated with this email. you can remove and wipe all the information of that device.   hope this information helpful