Merge old emails in Outlook

Merge pst software will help you to merge your multiple PST file into one single file and use that without wasting important time.
Professional Approach to Merge Two or Multiple Email Accounts into One in Outlook

Run the wizard and select the PST files.
Choose the Merge option.
Select option, merge in an existing PST, new PST or Outlook Profile.
Select mailbox items and hit the Next button.

Read more :- osttopstapp/pst-merge.html