Merging is the best technique to combine multiple numbers of PST file into single PST file. Merging of PST file can be done by using SysInfo PST Merge software, that is simple and reliable software that can merge multiple PST file into single PST file without modifying original PST. This software support Unicode PST and ANSI PST files and also removes the duplicity of mailbox items.

Get more info at:- http://migrateemails.com/combine-pst-files/