We have to shift our web-site to a new domain due to some unavoidable circumstances. The portal has been up and running there since 2009. It has good index in various search engines and we are getting a good number of page hits on daily basis.
Losing the search hits and index are our big concern. We are not sure how best we can handle this.
What all can be done to preserve as much as possible while shifting to new domain name.
If you're set up in Google's Webmaster Tools, you can explicitly tell them you're switching domains with the change of address utility on top of the usual 301 redirect stuff.
301 Redirect Old Pages to New Pages: Setting up a 301 Redirect will not only send the user to the correct page, but will also tell search engines that the page has been permanently been moved and it will transfer the link credit to the new page. Ideally, this should be done at page level: Each page of the old site should be redirected to the new site's equivalent url, mapping old-page to new-page.
Use the Change of Address Tool in Google Search Console (the rebranded name for Google Webmaster Tools), as mentioned in Su's post.
Bing has a similar Site Move tool, so use it too.
Update any important Backlinks where possible to point to the new site - use a backlink checker tool to find them
