A few steps have to be done to prepare for such a setup in Kentico:
1) Under Site Manager -> Settings -> URLs and SEO (devnet.kentico.com/docs/7_0/devguide/search_engine_optimization.htm), please enable Allow permanent (301) redirection.
2) In the same settings page, slightly below, please enable Redirect document aliases to main URL setting.
Please make sure the settings are correctly inherited in the particular site (and not only in global site scope - the drop-down list in the upper left corner will show what I mean)
3) If the original domain does not point to a running site any longer, you will need to add a domain alias to your site running within Kentico CMS instance (devnet.kentico.com/docs/7_0/devguide/index.html?managing_sites.htm - Domain aliases tab) and configure it to Redirect URL as shown in the example with macro expressions. Do not forget to include the macros shown in the example.
4) The last step you need to do is to add the corresponding document aliases with former alias paths (even those from under different domain) in the new site managed by Kentico CMS:
devnet.kentico.com/docs/7_0/devguide/document_properties_urls.htm - Document aliases, explained in more details at devnet.kentico.com/docs/7_0/devguide/multiple_document_aliases.htm