our exchange server and primary dc are in different location and the link speed is 5MB.But users are complaining that email send / receive is very slow. can we install new exchange server locally and users should connect to this server and it should synchronize with main exchange server in main location????

Why not place a domain controller in the same location as the Exchange server? You say "primary DC". How many domain controllers do you have? Exchange is constantly querying Active Directory (stored as replicas on the domain controllers) and the slow link (5 MB bandwidth on paper but actual throughput may be less) may contribute to the delay your users notice. That's my first reaction seeing your "exchange server and dc in different locations". They are in the same Active Directory site at least, right? * Also, does the Exchange server send and receive mail through the 5MB link that connects it to the primary domain controller or does it send email directly to the Internet via another link? * Trying to synchronize email between the two locations (possibly with a DAG, although I'm not sure the solution would be appropriate), may create even more congestion on the slow link.Please mark as helpful if you find my contribution useful or as an answer if it does answer your question. That will encourage me - and others - to take time out to help you.

we have two dc and exchange servers in other location. In our location only one dc is available

OK, so it should have a domain controller available in the same location. That's good. * What is slow: - users sending to other users in the same organization? - users sending to other recipients outside the company? - both? * How do you connect to the outside world? What kind of bandwidth do you have there? * What other kind of traffic is using the link between the two sites? * Rather than spending money on a second Exchange server that you may not need otherwise, not to mention licenses (Server license and CAL), you might better spend that money on upgrading the quality of your link. Please mark as helpful if you find my contribution useful or as an answer if it does answer your question. That will encourage me - and others - to take time out to help you.